add definition of m2w64_c_stdlib on windows

[h-vetinari]

As suggested by @isuruf. Compiler comes from here.

I don't know if this needs a corresponding m2w64_c_stdlib_version, please advise.

[conda-forge-webservices]

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.

[h-vetinari]

Just noticed that you're using

cross_target_stdlib_version:
  - 9
cross_target_stdlib:
  - m2w64-sysroot

in https://github.com/conda-forge/ctng-compilers-feedstock/pull/130/files. I don't know the m2w64 stack, but I'm guessing that m2w64-sysroot is closer to what we want for the stdlib than m2w64-toolchain?

[isuruf]

I don't know the m2w64 stack, but I'm guessing that m2w64-sysroot is closer to what we want for the stdlib than m2w64-toolchain?

That's still experimental.

[isuruf]

We also need to fix the piggy-back migrator

[h-vetinari]

We also need to fix the piggy-back migrator

Can you open an issue with what should be done on cf-scripts?

[isuruf]

See regro/cf-scripts#2547