Now that GCC 10.1 has been released and lang/gcc10 arrived to track
GCC 10 releases, switch to that over lang/gcc10-devel when GCC 10 is
requested.

Use lang/gcc11-devel when GCC 11 is requested, but note that this is
absolutely experimental and subject to constant change and likely
breakage over the next half year at least before that release series
enters stabilization. Use at your own risk.