For a long time orchestra has been struggling to make sure each
component was getting the C/C++ flags we wanted. Each build systems do
that differently. Morover, since we have certain "contradictory" options
for compile- and link-time, we have been having issues with build
systems building and linking in a single shot.

This commit radically solves this issue by introducing
`hard-flags-compiler-wrapper.py`, a wrapper script for compilers that:

1. Splits linking and compilation inspecting the command line.

2. Detects from environment variables which additional flags to
   pass. Depending on the name of the environment variable, the flag can
   be used only for a certain compiler (e.g., `clang`), only for a
   certain language (e.g., `cxx`) or only for a certain action (e.g.,
   "compile" vs "link").

This provides us the maximum flexibility and, since this new method is
"embedded" in the compiler, bypasses all the build systems
specific-issues.

Also, it significantly makes the description much more readable and
compact.

In case of failure, push the binary archives and fail, but do not
promote next-* branches.

In order to link against an old version of the glibc, we have to pass a
set of flags, some at compile time (CFLAGS), some at link-time
(LDFLAGS).

At compile-time, we set the sysroot to root/link-only, in order to have
the compiler look there first for header.
At link-time, we manually specify `-Lroot/link-only/lib` and reset
sysroot to /.
However, this often creates issues at configure-time, since in this
situation CFLAGS and LDFLAGS are often use at the same time, leading to
usage of / as sysroot.

This commit fixes the problem by ensuring that the `--sysroot` flag in
LDFLAGS will be available only to the link, by simply adding `-Wl,`.

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In ui/qt, we patch `linux-clang/qmake.conf` in order to build `qmake`
using the appropriate flags. However, these changes used to get
installed, leading to hardcoding paths from the CI.

This commit removes the offending lines after the install phase.

Sadly, QtCreator plugins need includes from QtCreator source code.  In
future, we'll need to be able to express dependencies on the source code
of other components. For now, just invoke `orc clone ui/qt-creator`.