Add flags to avoid string optimization

[hmaarrfk]

Fixes: https://github.com/conda-forge/ctng-compiler-activation-feedstock/issues/63

Questions:

• [ ] Do we need this in the FFLAGS. I assumed so.

Checklist

• [x] Used a personal fork of the feedstock to propose changes
• [x] Bumped the build number (if the version is unchanged)
• [x] Reset the build number to 0 (if the version changed)
• [x] Re-rendered with the latest conda-smithy (Use the phrase code>@<space/conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• [x] Ensured the license file is being packaged.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[hmaarrfk]

@conda-forge-admin, please rerender

[beckermr]

I can't recall if cflags gets reused for the other vars and so we only need this there.

I think @isuruf might have insight or we can consult the activation scripts.

[hmaarrfk]

A quick search of CFLAGS in https://github.com/hmaarrfk/ctng-compiler-activation-feedstock/blob/fno-merge-constants/recipe/activate-gfortran.sh#L88 reveals nothing.

[beckermr]

Right except that the Fortean compiler requires the c one maybe. In any case, duplicated flags are ugly but shouldn’t break anything I think.