Add gaea c6 config - Githubissues

Summary

Adding a gaea-c6 site config.

Note the interesting compiler flags. We want the Intel compilers to be aware of a recent-ish version of GCC for the usual reasons. On C6, GCC 12 and 13 are installed as 'gcc-12' 'gcc-13 'gfortran-12' etc., and using -gcc-name and -gxx-name appear to be the preferred ways of pointing to non-standard GCC executable names. That said, when I do that, ecmwf-atlas won't compile unless I also add -static-libstdc++, so I've added that. The alternatives would be to install our own GCC (my least favorite option), try a different version (not clear that this would work, like if we had the admins install GCC 11), or create aliases for the compilers so they use the regular names, then add that path to $PATH. For the last option, it would avoid the need for the -static-libstdc++ flag, but it's kind of an ugly solution.

Testing

Tested building 1.6.0 unified env, as well as concretizing and installing some packages based on develop.

Applications affected

all

Systems affected

gaea-c6

Dependencies

none

Issue(s) addressed

Related to #1130

Checklist

[x] This PR addresses one issue/problem/enhancement, or has a very good reason for not doing so.
[x] These changes have been tested on the affected systems and applications.
[x] All dependency PRs/issues have been resolved and this PR can be merged.

JCSDA / spack-stack

Add gaea c6 config #1132