store motion breaks asm outputs to memory

[Alexandre Oliva]

The following program:

int *p;
int f () {
  int ret;
  asm volatile ("%0" : "=m" (ret));
  if (ret != 0)
    *p = ret;
  return ret;
}

fails to compile with -mam33 -O2 on mn10300-elf.  The problem is that
the careful addressof expansion of the asm output operand, that would
have allowed it to compile, is annihilated by store motion: it
replaces with a pseudo the dest stack slot ``copied from'' the
ASM_OPERANDS.  The pseudo ends up being assigned to d0 by global
alloc, and reload barfs, complaining of inconsistent operand
constraints in the asm.

Here's a fix.  The first hunk is enough to fix the problem, but I
couldn't convince myself the second shouldn't remain.  Ok to install?