m68knommu: Handle multiple pending signals

we shouldn't bugger off to userland when there still are
pending signals; among other things it makes e.g. SIGSEGV
triggered by failure to build a sigframe to be delivered
_now_ and not when we hit the next syscall or interrupt.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>