gcc: Update patches submitted/merged upstream

I took 5 of our patches and submitted to upstream gcc. This highlighted that
patches 0026 and 0018 should be merged together and some tweaks were made to
try and make it acceptable to upstream. The other patches have their headers
updated to match what was submitted.

The libstdc++ option patch was also cleaned up ready for upstream as the
documentation wasn't quite right.

The CXXFLAGS_FOR_BUILD piece of 0026 is separated out into a new patch which
can be submitted separately to upstream.

Two of the patches have been merged, status updated accordinly.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>