lang/gcc11-devel: Update to the 20210619 snapshot of GCC 11.1.1

This brings three back ports for the arm back end, two for x86, and
five for powerpc, plus 10 for the middle end, four for the tree
optimizers and another four for various parts, five for the C and
C++ front ends each, three for Fortran, and a full 13 for libstdc++.

Also register a conflict with the new lang/gcc11 port.