mingw: Disalbe FORTIFY_SOURCE by default.

[shlevy]

In newer versions of mingw, programs compiled with FORTIFY_SOURCE need
to link to libssp or they will have link-time errors.

gmp has been broken since @pstn updated mingw-64 in c60a0b0

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• 21.11 Release Notes (or backporting 21.05 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.

[SuperSandro2000]

In newer versions of mingw, programs compiled with FORTIFY_SOURCE need
to link to libssp or they will have link-time errors.

Would an alternative be to just add libssp or am I missing something?

[shlevy]

@SuperSandro2000 We'd have to add it to all links with fortify enabled, but just adding -lssp when fortify is given results in failed autoconf checks. Would need to track down the proper fix.

[Ericson2314]

@alexfmpe and I were looking into this (see #132199). I think this is a good temp fix. I hope to fix it more properly with #132343 (which has been a long time coming!).

[alexfmpe]

@SuperSandro2000 We'd have to add it to all links with fortify enabled, but just adding -lssp when fortify is given results in failed autoconf checks. Would need to track down the proper fix.

That's more or less the conclusion I reached in #132188 (comment)

[pstn]

Just for the record: I did not break pkgs.gmp as would be discoverable by nixpkgs-review, as @shlevy seems to feel the need to imply constantly. I assume some cross package he uses broke.

[shlevy]

@pstn Apologies for the lack of precision, I did mean gmp cross-compiled to mingw in that commit.

I don't know what you mean by "feel the need to imply constantly." I just put that in one commit message to explain why this was needed now and not before.