gcc-runtime: Move content from gcclibdir into libdir

OE does not use the traditional /usr/lib/gcc prefix to store gcc-runtime
it basically is moved into libdir, however some newer files were
installed by newer versions of gcc especially libgomp ( omp.h openacc.h )
into gcclibdir, so we have content in both directories, this confuses
other tools which are trying to guess the gcc installation and its
runtime location, since now we have two directories, the tools either
choose one or other and we get inconsistent behavior, e.g. clang for
aarch64 uses /usr/lib but same clang for riscv64 chose /usr/lib/gcc

This change ensures that OE ends up with single valid location for gcc
runtime files

Move more common bits into common inc file

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>