Goal

• Provide a convenient and (eventually) supportable way to change the built-in defaults of /usr/bin/gcc, /usr/bin/g++, /usr/bin/gfortran.
• These changes should be effective independently of the build system, and similar to what GCC already supports at configure time using the --with-arch_64= option. (However, it should not be implemented as a separate build of GCC.)

Acceptance Criteria

• When building extensions, pip install should switch to the new architecture level automatically.
• The configuration survives updates of the gcc, gcc-c++, gcc-gfortran packages.
• By default, the build flags should be upgraded to -march=x86-64-v3 for all language front ends.
  EDIT This was relevant when the target release was still RHEL 9.
• There should be a way to use -march=native instead.
• Maybe there should be a way to configure the override to use the latest installed GCC Toolset version (if any).