lang/gcc14-devel: Fix conflict on libgccjit.h and libgccjit++.h

Some GCC ports install libgccjit.h and libgccjit++.h in the
same directory.

Fix conflict for lang/gcc14-devel.

See also commit 0338e04504ee269b7a95e6707f1314bc1c4239fe that fixed the
conflict in the same way for lang/gcc11.

PR: 257060, 277383