nix: force make to use old-style two-pipe-fds jobserver

gcc lto-wrapper uses the make jobserver to speed up linking, and it
doesn't support the new fifo:/path style of jobserver-auth yet. it'll
still work but use only one thread, so we should stick to the old style
for now.

pkgs/tools/package-management/nix/common.nix

@@ -181,6 +181,10 @@ self = stdenv.mkDerivation {
   ];
 
   makeFlags = [
+    # gcc runs multi-threaded LTO using make and does not yet detect the new fifo:/path style
+    # of make jobserver. until gcc adds support for this we have to instruct make to use this
+    # old style or LTO builds will run their linking on only one thread, which takes forever.
+    "--jobserver-style=pipe"
     "profiledir=$(out)/etc/profile.d"
   ] ++ lib.optional (stdenv.hostPlatform != stdenv.buildPlatform) "PRECOMPILE_HEADERS=0"
     ++ lib.optional (stdenv.hostPlatform.isDarwin) "PRECOMPILE_HEADERS=1";