Fix build on darwin_arm64 (Apple M1) (digital-asset#13951)

Co-authored-by: Claudio Bley <[email protected]>

nix/bazel.nix

@@ -30,9 +30,14 @@ let shared = rec {
  zip
  ;
 
- ghc_lib_deps = pkgs.buildEnv {
+ # ghc-lib needs GHC 8.6.5, but the first version to support Darwin arm64 /
+ # Apple M1 is GHC 8.10.7. Use GHC 8.6.5 on aarch64_darwin via Rosetta to build
+ # the ghc-lib cabal sdist.
+ ghc_lib_pkgs = if system == "aarch64-darwin" then import ./nixpkgs.nix { system = "x86_64-darwin"; } else pkgs;
+
+ ghc_lib_deps = with ghc_lib_pkgs; buildEnv {
  name = "ghc-lib-deps";
- paths = with pkgs; [
+ paths = [
  autoconf
  automake
  cabal-install
@@ -41,15 +46,15 @@ let shared = rec {
  gnumake
  ncurses
  perl
- pkgs.haskell.compiler.ghc865Binary
+ haskell.compiler.ghc865Binary
  stdenv.cc # ghc-lib needs `gcc` or `clang`, but Bazel provides `cc`.
  xz
  ] ++ (
  if stdenv.isDarwin
  then [stdenv.cc.bintools.bintools xcodebuild]
  else []
  );
- ignoreCollisions = pkgs.stdenv.isDarwin;
+ ignoreCollisions = stdenv.isDarwin;
  };
 
  postgresql_10 = if pkgs.buildPlatform.libc == "glibc"