Create meson_cross_file.txt for cross compilation

[h-vetinari]

Based on what exists in https://github.com/conda-forge/clang-compiler-activation-feedstock + conda-forge/clang-compiler-activation-feedstock#100, in order to solve cases like conda-forge/scipy-feedstock#205; numpy, scipy & pandas are all moving to meson, so we'll need to sort this out eventually.

I admit that I don't know the ins & outs of this feedstock, it's very possible that this needs further work.

[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.

[isuruf]

You should also add https://github.com/conda-forge/clang-compiler-activation-feedstock/blob/a9f5382dbd3d753aa0a8d27a8c0575c6ee4ea363/recipe/activate-clang.sh#L145

[isuruf]

Thanks

[github-actions]

Hi! This is the friendly conda-forge automerge bot!

I considered the following status checks when analyzing this PR:

• linter: passed
• azure: passed

Thus the PR was passing and merged! Have a great day!