"Revert" Intel deprecation flag changes in spack's lib/spack/env/cc and pull in improved solution from spack mainline

[climbfuji]

Summary

This PR resolves #1230. Detailed information on what this PR does and why it is necessary is given in the issue. The improved solution does away with having to specify the diag-disable flags, since these are now set implicitly (and only during spack environment builds, not in downstream applications). Credits to Peter Scheibel from the spack core team for suggesting it and adding the spack unit tests to my implementation.

Testing

• CI (with oneapi using icx, icpx, ifort and with intel using icc, icpc, ifort)
• Manual testing on Dom's development machine (blackpearl; with [email protected] using icx, icpx, ifort)

Applications affected

None

Systems affected

All using recent Intel compilers

Dependencies

• waiting on Replace previous solution to suppress Intel's deprecation warnings with spack-blesssed version spack#460

Issue(s) addressed

Resolves #1230

Checklist

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

[RatkoVasic-NOAA]

Looks good to me.