Multi-toolchain support for C++

[antonkri]

Acceptance criteria:

• Enable multiple toolchain instantiations in one MODULE.bazel file
• Official release of Linux toolchain with support for x86_64 and arm and execution of unit-tests
• Official release of QNX toolchain with support for x86_64 and arm
• Base setup of compiler flags and an interface to set additional flags for every module additionally.
• Official documentation

What should we achieve for v0.5-beta release

• baselibs and communication modules are using the new toolchain
• reference integration is using the new toolchain for compilation and building the binary and the old toolchain for creating ifs image.

As soon as this ticket is solved, we will need separate tickets for all areas to switch to the newest version.

[anmittag]

@nradakovic will this be part of the v0.2.3?