Since $(AS) is the assembler, passing it a list of preprocessor include
flags doesn't make much sense. The files aren't preprocessed which means
`#include` lines aren't respected, and while it would affect `.include`
usage, we never use that, and it's extremely unlikely to change. Plus,
it's extremely unlikely we'd have .s files in common places to include vs
contained entirely within a specific arch dir, and at that point, it can
be included directly (with no flags), or the arch can add the unique set
of include paths that it needs for itself.
These subdirs have unique configure scripts to do some compiler tests.
The checks should work for all targets, so hoist them up to the top
libgloss dir. This should allow us to delete these subdir configure
scripts.
It means the top-level gains autoheader support, but that's fine.
It wasn't exporting any defines previously (i.e. -D into CPPFLAGS),
and all of the defines it now exports are only used by code in the
libnosys subdir which was expecting to have a config.h.
