Motivation for this change

• Add enableShared and enableStatic arguments for boehmgc, along with configureFlags additions overriding the default flags when those arguments are overridden.
• Remove the musl-dependent --disable-static option, as that is the default behavior.
• Building with pkgsStatic or pkgsMusl was failing to produce the debug output, so disable separateDebugInfo for musl hosts.
• Add an override to pkgsStatic which builds boehmgc with enableShared disabled and enableStatic enabled.

I haven't really tested any of this yet, because other packages in the dependency graph for my project do not build using pkgsStatic.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• 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 pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc @