Add linux/elfcore-compat.h

Add linux/elfcore-compat.h

This adds the linux/elfcore-compat.h header file, which is the CONFIG_COMPAT
analog of the linux/elfcore.h header.  Each arch that needs to fake out
fs/binfmt_elf.c for its compat code can use this header to replace the
hand-copied definitions of the compat variants of struct elf_prstatus et al.
Only the pr_reg field varies by arch, so asm/{compat,elf}.h must define
compat_elf_gregset_t before linux/elfcore-compat.h can be used.

It's a clean-up that every arch with compat core dumping code can benefit
from.  I only touched the ones I have handy to test at home.  Doing the same
for each other arch should be straightforward, and I'm happy to offer tips.

Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Andi Kleen <ak@suse.de>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>