gcc: disable symlink checks on cross + nolibc for now

This is a hack, but a proper fix requires an stdenv rebuild,
so it will have to go to staging.

pkgs/development/compilers/gcc/common/builder.nix

@@ -3,6 +3,7 @@
   stdenv,
   enableMultilib,
   targetConfig,
+  withoutTargetLibc,
 }:
 
 let
@@ -314,4 +315,7 @@ originalAttrs:
       done
     '';
   }
+  // lib.optionalAttrs ((stdenv.targetPlatform.config != stdenv.hostPlatform.config) && withoutTargetLibc) {
+    dontCheckForBrokenSymlinks = true;
+  }
 ))