libcxx: update to 10.0.0

Switched to upstream tarballs.

Switched to libcxxabi as using libsupc++ is quite wonky.

Fixed description.

Removed patches. The fixes are cosmetic.

Added ssp patch. This one is needed for i386 and powerpc under musl.

Compile tested every C++ package in the tree with the exception of
several boost packages. There's something broken with boost.

Ran tested with gerbera.

Signed-off-by: Rosen Penev <rosenp@gmail.com>