mosml: pass -fpermissive to C compiler

[athas]

The MosML build system relies on some terrible C that GCC 14 now refuses to compile. This has supposedly been fixed in MosML upstream, but the fix is not yet in any released version. It is not so easy to simply cherry-pick the changes necessary to make GCC 14 work, since they seem spread over various different commits. The hacky solution in this PR serves to make this rather obscure derivation work for a little while longer.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[paparodeo]

https://gcc.gnu.org/gcc-14/porting_to.html

add env.NIX_CFLAGS_COMPILE = "-fpermissive"; makes the build work with gcc-14. no need to pin to 13

perhaps better, only disable the new gcc-14 errors

  env.NIX_CFLAGS_COMPILE = toString (
    map (x: "-Wno-error=${x}") [
      "declaration-missing-parameter-type"
      "implicit-function-declaration"
      "implicit-int"
      "incompatible-pointer-types"
      "int-conversion"
      "return-mismatch"
    ]
  );

[athas]

I have updated the PR to use env.NIX_CFLAGS_COMPILE = "-fpermissive"; instead. I think it likely that future C compilers will find other parts of the ancient MosML code base objectionable.