buildGoModule: Introduce ldflags argument

[infinisil]

Motivation for this change

Previously it was not possible to define multiple ldflags, since only
the last definition applies, and there's some quoting issues with
buildFlagsArray. With the new ldflags argument it's possible to do
this, e.g.

ldflags = drv.ldflags or [] ++ [
  "-X main.Version=1.0"
]

can now properly append a flag without clearing all previous ldflags.

Pretty much fixes #112054, ping @jtojnar @Mic92 @kalbasit @kvtb

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 pkgs 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/)
• Added a release notes entry if the change is major or breaking
• Fits CONTRIBUTING.md.

[r-rmcgibbo]

Result of nixpkgs-review pr 125520 at be257e24 run on aarch64-linux 1

3 packages marked as broken and skipped:

• gb-backup
• linuxPackages_testing_bcachefs.oci-seccomp-bpf-hook
• secretscanner

696 packages skipped due to time constraints:

• _3mux
• act
• age
• air
• alertmanager-bot
• alertmanager-irc-relay
• amass
• amfora
• antibody
• archiver
• ...

4 packages built successfully:

• nixopsUnstable
• poetry
• rmfuse
• yj

[kalbasit]

Can this be backported to 21.05 or is it too late?

[zowoq]

Can this be backported to 21.05 or is it too late?

I think backporting this would be fine and may even be somewhat necessary so that go package backports aren't a hassle.

[zowoq]

I won't be doing the backport myself but I'd suggest that it be backported with #125597 to limit the number of rebuilds.

[terinjokes]

@zowoq Should it be backported with the next Go release then?