[clang] [clang] Updating to include gcc-toolsets 13 and 14 (PR #128438)

[Nikita Popov via cfe-commits]

nikic wrote:

@MaskRay We already do that, with the following content in the config file:
```
%if %{defined gts_version}
%global cfg_file_content %{cfg_file_content} --gcc-install-dir=/opt/rh/gcc-toolset-%{gts_version}/root/%{_exec_prefix}/lib/gcc/%{_target_cpu}-redhat-linux/%{gts_version}
%endif
```

I suspect that this change may be about people building their own clang (not the one RHEL ships) and wanting to use GCC toolset. Would be good to clarify what exactly the motivation is.

https://github.com/llvm/llvm-project/pull/128438