`compilers.yaml` not generated when gcc version is shadowed by system gcc

[bcumming]

When the version of gcc in the gcc compiler toolchain matches the system-provided compiler, the compiler is not found when generating compilers.yaml for any spack environment that requests the gcc compiler toolchain.

This is observed on a system with gcc 11.3 in /usr/bin, when [email protected] toolchain is requested to install nvhpc or an environment in environments.yaml.

It looks like the version found in compilers/gcc environment matches the one in config/compilers.yaml, so it is skipped for some reason. This is either a Spack bug, or misuse of Spack by us.