Move sysdeps/gnu/unwind-resume.c to sysdeps/generic/unwind-resume.c

This change allows architecture-specific sysdeps directories to override
it.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

diff --git a/sysdeps/gnu/unwind-resume.c b/sysdeps/generic/unwind-resume.c
similarity index 100%
rename from sysdeps/gnu/unwind-resume.c
rename to sysdeps/generic/unwind-resume.c