Search compiler-specific fpm builds

[perazz]

Attempt to fix #37 fortran-lang/fpm#1104

fpm release assets were changed naming in fortran-lang/fpm#985.

@gnikit should we bump the release version after this? Otherwise, people won't be able to use fpm 0.11.0 and in general those using latest wuold break their CIs.

[certik]

Yes, make a new release of setup-fpm. So that the last version works with fpm < 0.11.0 and the new version with fpm >= 0.11.0. Document this in the README.

[certik]

Also, very important: allow setup-fpm to select an exact version of fpm, and make that the default main example in the README. People should have been using that already, that way things will not break like this.

[certik]

Goal: a specific version of setup-fpm and fpm together should never break at the CI.

We can do backwards incompatible changes, and users can manually upgrade both setup-fpm and fpm to compatible "combo" versions. That's fine.

[perazz]

right now the default version is latest which I think will always break something in the long run. So maybe each setup-fpm version should instead have a default fpm version it works well with? Then we should make a table in README that shows the default fpm version for each version of the action?

[perazz]

Thank you @gnikit @certik, merging.

[certik]

Yes exactly --- default version by default, and users can override it manually. Then things should never break on its own.