lang/gcc11-devel: Update to the 20210501 snapshot of GCC 11.1.1

This is the first snapshot after the GCC 11.1 release.

It brings two back ports for the RTL optimizers, one each for the
tree optimizers and debug information, two for the arm back end,
five for aarch64, two for x86 and one for powerpc, plus two for
the Fortran front end, four for C++ and five for libstdc++.