Allow non-universal macOS builds also on base-browser

Doesn't work 🙁 .

pierov@tb-build-05 ~/b/tor-browser-build (main)> rbm/rbm build release --target testbuild --target browser-macos-x86_64 --target basebrowser
Error: Missing filename:
{
  name => "[% c(\"var/compiler\") %]",
  project => "[% c(\"var/compiler\") %]",
}