graphite2: fixup build on aarch64-darwin after PR #123420

See the PR for discussion.  This caused thousands of build regressions.

pkgs/development/libraries/silgraphite/graphite2.nix

@@ -20,7 +20,8 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [ pkg-config cmake ];
   buildInputs = [ freetype ]
-    ++ lib.optionals (!stdenv.cc.isGNU) [ libgcc ];
+    # On aarch64-darwin libgcc won't even build currently, and it doesn't seem needed.
+    ++ lib.optionals (with stdenv; !cc.isGNU && !(isDarwin && isAarch64)) [ libgcc ];
 
   patches = lib.optionals stdenv.isDarwin [ ./macosx.patch ];