Prevent mixing compilers in Spack versions over 1.1.0

[chapman39]

This sets an option recently added in Spack. By default Spack allows mixing compilers. However, it can lead to some unexpected builds if for example you build some packages with GCC and others with Clang. So, this PR disables compiler mixing by default in Uberenv. However, you can use command line option --spack-compiler-mixing, if you want the default Spack functionality.

Depending on what options are set, the following output and spack.yaml section will be added:

[enable/ disabling mixing compilers in Spack]

spack.yaml

  concretizer:
    compiler_mixing: true/ false

I have tested this in Smith, and it works as expected.

Also, I created a simple version2tuple function. That way, we can compare version strings. This helps in these sorts of situations where we need to check if a Spack version is above/ below a certain threshold.

More info:

• https://spack.readthedocs.io/en/latest/configuring_compilers.html#mixing-compilers
• concretizer: option to disable compiler mixing between runtime deps spack/spack#51135

[chapman39]

@scheibelp for awareness

[chapman39]

putting on draft until i can get smith to concretize with this setting

==> Error: failed to concretize `smith@develop+devtools+profiling %[when='%fortran'] fortran=gcc %[when='%c'] c=clang %[when='%cxx'] cxx=clang %[when='%mpi'] [email protected]_19` for the following reasons:
     1. Compiler mixing is disabled

[adrienbernede]

I have the same error on my end with quandary.

[white238]

Fix in spack/spack#51796