Fixes for the following things that caused errors in the translated
module due to changes introduced in the `prune-eh` optimization pass:

- `Support.c` is now compiled with support for exceptions, to avoid
  marking the `raise_exception_helper` function to be marked `unwind`
  during the link phase.
- Added a fake `ret` at the end of the `catchblock` to avoid
  optimizations.
- Marked the `invoke` instructions not as candidate for function
inlining.

`revcc` is a simple script that forwards its arguments to a specified
compiler, except in the case in which the compiler is asked to link the
final program. In such case, the compiler is invoked as appropriate, but
the resulting binary is then translated using rev.ng and replaced by the
translated version.

Fix for a situation where the fallthrough basic block of an instruction
calling a helper function is not in an executable segment and therefore
not created.

Quick fix to detect overflow in SET interval computation.

This commit fixes a huge performance issue due to performing a orphan
basic block cleanup every time `JumpTargetManager::peek` was called
instead of only when actual harvesting was required.

Now using the `root` function of the cloned module as a starting point
for the isolation process.

In this way we can ignore the old module, and in particular we can
drop the `ModuleCloningVMap`, a giant map that was used to keep the
match between old and new global objects and was used in the instruction
cloning phase.

Also changed the creation of the trampoline for the isolated function,
using a new basic block and later purging all the unreachable basic
blocks in the `root` function.

Moved the definition of `OBJ` before its first use.

Moved the definition of `CSV` outside the lifting scope, to avoid
erroneous behaviors when invoking the script with the `-s` option.

This commit uses SET, information about canonical values and labels to
detect if an indirect function call is targeting an external symbol.

The strings used for the name of external symbols are uniqued global
variables. This commit also uses this approach for the disassembly of
original instructions, which used to be metadata.

So far we've been tracking only base-relative relocations in an ad-hoc
fashion. This commit introduces a data structure that can describe the
most common relocations, including those for `.got`, `.got.plt`,
base-relative and `R_*_COPY`.

A label describes a range of the binary. A label can be generated from a
symbol (basically assigning a name to range of the binary) or from a
relocation, describing the content of a certain range.

This commit generates labels from symbols and relocations, including
MIPS implicit relocations.

This commit also introduces canonical values.

A register can have a canonical value, i.e., a value that register will
assume when the analyzed module is being run. This is typically useful
for the value of the global pointer, which is different from one module
to another but, within a module, is stable.

This commit registers the canonical value of `gp` (in MIPS), if
available.

`segments_count` provides a way for the runtime to know how many
executable segments the original program had. This is used to implement
the `is_executable` function.

While the `segment_boundaries` contained only the executable segments,
`segments_count` included non-executable segments too, leading to an
out-of-bound read which sometimes led to a spurious `Unknown PC` error.

While translating the code, it might happen that a basic block needs to
be splitted and the second part to be revisited. In such cases, the
second part is register for being "purged" at the next iteration.

Translation failed if we met such a basic block before purging. This
commit correctly handles such situations.

In certain cases we find more than one instruction storing the return
address to a register. In particular, this happens with a `bltzal`
instruction in MIPS, where the return address is stored both in `ra` and
`btarget`.

For now, do not consider these as actual function calls.

We used to check if the address associated to the `PT_DYNAMIC` program
header matched the one of the `.dynamic` section. However, we were not
recording it, which is required in case sections headers are
missing/corrupt.

In QEMU we should suppress the emission of the debug_insn
pseudo-instruction (which delimits the tiny code instructions
corresponding to an original input instruction) in case of a delay slot.

However, this was not happening due to a wrong `#ifdef`. Since this has
now been fixed in QEMU, this commit updates the results of the tests
accordingly.

`DebugAnnotationWriter` creates debug information for each instruction
in the generated LLVM IR module. Before this commit, it used to clobber
any debug information in any function, which lead to wrong debug
information on helper functions.

This commit ensures that debug information of helper functions are
untouched, so that they can be used while debugging.

Updating to LLVM 7 mainly involved the following steps:

* Upgrade APIs for folding ConstantExpr.
* Upgrade APIs for GraphTraits.
* Upgrade APIs for DominatorTreeBase.
* Upgrade APIs for BinaryFormat to parse ELFs.
* Fix the LLVM Linker to properly link the QEMU helpers.
* Disable the new optnone attribute even with optimization -O0. This is
  necessary to allow SROA to do its job properly.
* Upgrade APIs to delete Instructions.
* Properly cleaning up orphaned metadata still referring to Instructions
  that have been destroyed. Recent versions of LLVM are more strict in
  this respect, and will assert when compiled in debug.
* Avoid using LLVM `getGlobalContext` which has been removed from newer
  versions of LLVM.
* Upgrade tests to use the new APIs.
* Upgrade APIs for instruction iterators and reverse iterators.

A method in RDA was returning nullptr when a basic block *had* a color
and a dangling reference when it did not.

This commit reimplements the (conditional) reaching definitions passes
as an instance of a monotone framework.

The `ConditionNumberingPass` has also been reworked in the way it
exposes its results, but it's otherwise unchanged.

A proper unit testing framework is also available to ensure everything
works as supposed to.

An `assert` used to check the type of a deleted object. This commit
delays the deletion of such object.

In case of a top `BoundedValue` which appears to be used with an
inconsistent signedness, simply change the signedness and keep it to
top.

This message used to be emitted unconditionally. It is now emitted only
as appropriate.

This commit introduces a new logger that prints out the name and reason
for each newly registered basic block.