Serialization (in the form of the `revamb.jt.reasons` metadata) of the
reason why a certain address is a jump target has been moved from
`JumpTargetManager::finalizeJumpTargets` to a new function
(`JumpTargetManager::createJTReasonMD`) which is invoked after the
function boundaries detection algorithm has been run.

`JumpTargetManager::translateIndirectJumps` has been pushed into
`JumpTargetManager::finalizeJumpTargets`. Moreover, an safety check
about the removal of `exitTB` has been introduced.

The basic block handling the default case of the dispatcher used not to
be tagged with `revamb.block.type`, now it is.

This commit introduces the `head` and `clear` methods for `QueueImpl`
(i.e., `UniquedQueue` and `OnceQueue`).

* QuickMetadata has been expanded to get a `MDString` or a `MDTuple`
  from a `StringRef`.
* Introducing `skipCasts`, which, given a `Value`, returns the innermost
  part of the expression, skipping over casts.
* Introducing `isCallTo`, which, given an `Instruction`, returns whether
  it's a call to a specific function or not. `getCallTo` is a sister
  function to be used in `if` statements.
* Moving `skip` and `erase_if` in `ir-helpers.h` so that all the
  translation unit can benefit from their usage.

`alloca` instruction are passed as variadic arguments to `newpc` to
prevent the optimizer from moving code around them. We used to cast them
all to `i8*`, however these casts where breaking the convention of
having all the `alloca` instructions at the beginning of the function.

Since these casts were not really necessary, they have now been dropped.

This commit introduces a new metadata (`revamb.jt.reasons`) containing a
list of reasons why the initial PC of the current basic block has been
identified as a jump target.

This commit fixes an assertion triggered by the fact that a segment
includes exclusively zero-initialized data (i.e., size on file is 0,
memory size is not). In this case LLVM detects the fact that the global
variable associated to the segment is composed exclusively composed by
0s and uses a `ConstantAggregateZero` as an initializer instead of a
`ConstantDataArray`.

Currently the solution is ignore that data, however, in the future it
might be beneficial to be able to read data from `.bss`, even if we just
have zeros there.

Thanks to Thorbjoern Schulz for reporting this bug.

This commit fixes some warnings given by GCC 6.3.0.

* Some `assert(false)` are not recognized as `noreturn`ing. They have
  been replaced with `llvm_unreachable`.
* Added `-Wno-ignored-attributes`: attributes are not part the function
  name mangling, and therefore they might create some problems when they
  are involved in template arguments. We don't care.
* Specializations of `readPointer` functions in `binaryfile.h` are now
  `inline`, so they don't appear as "unused" functions.

QEMU marks each input instruction with a special
pseudo-instruction. This commit makes revamb ignore such instructions
coming after a write to a `btarget` variable, which is an indication
that a delay slot is starting. In this way, the instruction will look
larger and re-translating part of it will not break the branch
instruction.

This simple commit should improve performance of the generated program
sensibly. Basically all the global variables will have internal linkage
from now on (unless the `--external` parameter is specified on the
command line). This way, the compiler will be able to avoid load/store
instructions when leaving code in the current translation unit.

In `translate -O2` we optimize the LLVM IR both with `llc` and
`opt`. However due to a bug in `translate`, `opt` was invoked but its
output was never used.

Introduce the `-disable-machine-licm` argument when the `translate`
script invokes `llc` with `-O2`.

We used to assert that a `BoundedValue` must not have any entries in the
`Bounds` field before translating a `boost::icl` interval to a
`BoundedValue`. However, if the `Value` associated to the `BoundedValue`
is a `Constant`, we might have an entry in `BoundedValue::Bounds`
immediately after constructing the object. This commit fixes this
problem by simply updating the assertion and clearing the field before
re-populating it.

This commit introduces a docs target which translates `.rst` files into
man pages or HTML documents and installs them in `/usr/share/man/man1`
or `/usr/share/doc/revamb`.

Update `GeneratedIRReference.rst:` to reflect recent changes to the
`root` function. Specifically, the presence of the stack pointer
argument and initialization of the program counter and the stack
pointer.

`FromIRToExecutable.rst` has been updated too, to take into account the
new way we link `support.c`.

Finally, the `--tracing` argument has been removed from
`RevambUsage.rst` and the `-trace` argument is no documented in
`TranslateUsage.rst`.

To compare strings, `STREQUAL` should be used, not `EQUAL`. This
prevented some inaccurate GCC warnings to be considered as non-errors.

While materializing values in SET through the `OperationStack` we used
to use as a type the type of the value associate to the currently used
`BoundedValue`. This was wrong, this patch uses the type on the free
operand on the top of the `OperationsStack` to perform the required
computations.

Landing pads are basically the `catch` blocks in C++ `try`/`catch`
statements. So far we were missing them since they are encoded in a
particular way in a way similar to DWARF debugging information in the
`.eh_frame` and, more specifically, in the `.gcc_except_table` sections
of ELF programs.

This commit parses these sections so that the basic blocks associated to
landing pads are correctly identified. Personality functions are
detected too. A test is also introduced to assess the effectiveness of
our code.

Since we now support disjoint ranges in ORSA, let's test it. This commit
also introduces some license disclaimers in tests assembly files.

`OSRA:handleComparison` was too big and complex, it has been mostly
rewritten.

* Create `OSRA::identifyComparisonOperands` which expands the argument
  of the comparison in a list of possible values (constants or
  OSRs). The new way in which we handle possible operands also fixes a
  bug showing up in case a constant OSR was being compared with an LLVM
  constant, which was checked for being a tautology/contradiction,
  preventing the reaching definitions of the operand to be considered
  too.
* Squeeze more information from uge/ugt. Unsigned comparisons lead to
  two pieces information: the result of the comparison itself, and the
  fact the left-hand side is greather than or equal 0. This secondo
  information is precious, but we were not able to exploit it in the
  case the original comparison is already "greater than" or "greater
  than or equal". In fact, `x - 4 > 10` gives us `x >= 4` and `x > 14`,
  which boils down to `x > 14`.  This commit introduces a change that
  handles this case as `NOT x - 4 <= 10` leading to the negation of `x
  >= 4` and `x < 14` which is way more informative.
* Improve `OSRA::mergePredicate` and `OSRA::applyConstraints`
  interfaces.
* In case a comparison instructions leads to multiple constraints on the
  same `Value`, these constraints are now first or-merged together and
  then propagated. This change improves the quality of the analysis in
  certain situations.

This commit introduces radically changes the implementation of
`BoundedValue`: it no longer represents a single, contiguous range, but
an arbitrary number of ranges.

The bounds are now represented through a
`llvm::SmallVector<std::pair<uint64_t, uint64_t>, 3>`.

* Introduce the `BoundedValue::bounds()` method, which allows to iterate
  over all the ranges that a `BoundedValue` represents. The `bounds`
  method returns a `Bounds` object, which can be used as a range
  composed by `BoundsIterator`.
* All the methods dealing with the `BoundedValue`'s bounds have been
  rewritten.
* New debugging information: "bv-merge". Print all the computations
  performed by `BoundedValue::mergeImpl`.
* Drop dead code: `BoundedValue::setBound` and `isPositive`
* Introduce `BoundedValue::isRightOpen` and drop
  `BoundedValue::isSingleRange`

Some subtle bugs have been fixed in `OSRA::pathSensitiveMerge`:

* Do not alter the current `BoundedValue` if merging a component would
  lead to bottom.
* Do not deactivate a reacher in case an incoherent condition is met.

In our reaching definition analysis we used to consider all the loads
not reached by any store as definitions. However we forgot to actually
register them as such, with the result that two consecutive loads from
the same CSV would end up being two free loads.

In `ConditionNumberingPass` we used to consider as resetting the last
basic block possibly interested in a certain numbered
condition. However, what we really meant, was that its successors were
resetting basic blocks. This commit fixes this issue.

`OSR::constant()` used to forward the result of
`BoundedValue::constant()`, but this is wrong, since the factor and the
base value have to be considered too.

or-merging bottom with anything used to produce a bottom value, which is
wrong. The non-bottom value should be produced instead.

Constraints associated to a memory instruction are propagated to
reached loads. However, if a constraint on the same `Value` is already
present, the new constraint should be and-merged, not or-merged.

* Introduce some additional helpers
* Spread some `const`ness
* Improve documentation
* New debugging information: "osr-bv". Prints every update operation
  performed in `BVMap::update`.
* Remove dead code
* Whitespace fixes
* Some new TODOs
* Fix some typos in comments