gdb: rename gdbarch.c to gdbarch-gen.c

For clarity and symmetry with `gdbarch-gen.h`.  I wouldn't mind
if all generated files had the `-gen` suffix.

Change-Id: Icb70194fb0e3e2fa9d1c6f0d9331be09b805b428
Approved-By: John Baldwin <jhb@FreeBSD.org>
3 files changed