build2: use lld from llvm 16 to link on darwin

pkgs/development/tools/build-managers/build2/bootstrap.nix

···
 { lib, stdenv
 , fetchurl
 , pkgs
+, buildPackages
 , fixDarwinDylibNames
 }:
 stdenv.mkDerivation rec {
···
 
   propagatedBuildInputs = lib.optionals stdenv.targetPlatform.isDarwin [
     fixDarwinDylibNames
+
+    # Build2 needs to use lld on Darwin because it creates thin archives when it detects `llvm-ar`,
+    # which ld64 does not support.
+    (lib.getBin buildPackages.llvmPackages_16.lld)
   ];
 
   doCheck = true;
···
     runHook preInstall
     install -D build2/b-boot $out/bin/b
     runHook postInstall
+  '';
+
+  postFixup = ''
+    substituteInPlace $out/nix-support/setup-hook \
+      --subst-var-by isTargetDarwin '${toString stdenv.targetPlatform.isDarwin}'
   '';
 
   inherit (pkgs.build2) passthru;

pkgs/development/tools/build-managers/build2/default.nix

···
 , fixDarwinDylibNames
 , libbutl
 , libpkgconf
+, buildPackages
 , enableShared ? !stdenv.hostPlatform.isStatic
 , enableStatic ? !enableShared
 }:
···
   # LC_LOAD_DYLIB entries containing @rpath, requiring manual fixup
   propagatedBuildInputs = lib.optionals stdenv.targetPlatform.isDarwin [
     fixDarwinDylibNames
+
+    # Build2 needs to use lld on Darwin because it creates thin archives when it detects `llvm-ar`,
+    # which ld64 does not support.
+    (lib.getBin buildPackages.llvmPackages_16.lld)
   ];
 
   postPatch = ''
···
 
   postInstall = lib.optionalString stdenv.isDarwin ''
     install_name_tool -add_rpath "''${!outputLib}/lib" "''${!outputBin}/bin/b"
+  '';
+
+  postFixup = ''
+    substituteInPlace $dev/nix-support/setup-hook \
+      --subst-var-by isTargetDarwin '${toString stdenv.targetPlatform.isDarwin}'
   '';
 
   passthru = {

pkgs/development/tools/build-managers/build2/setup-hook.sh

···
         $build2ConfigureFlags "${build2ConfigureFlagsArray[@]}"
     )
 
+    if [ -n "@isTargetDarwin@" ]; then
+        flagsArray+=("config.bin.ld=ld64-lld")
+        flagsArray+=("config.cc.loptions+=-fuse-ld=lld")
+        flagsArray+=("config.cc.loptions+=-headerpad_max_install_names")
+    fi
+
     echo 'configure flags' "${flagsArray[@]}"
 
     b configure "${flagsArray[@]}"