Restore INDIRECT_REF asm operand heuristic with MEM_REF

As noticed we are looking for INDIRECT_REF with allows_mem to avoid
a copy since then we're sure the operand is in memory (assuming
*& is folded).  But INDIRECT_REFs are no longer a thing, the following
replaces the check with a check for a MEM_REF with a non-ADDR_EXPR
operand.  This should fix the regression part without fully
exploring all possibilities around tcc_reference operands.

I've placed an assert that we do not see an INDIRECT_REF here.
While we gimplify asm operands we never do any checking on its
IL afterwards.

2022-03-09  Richard Biener  <rguenther@suse.de>

	* cfgexpand.cc (expand_gimple_asm): Special-case MEM_REF
	with non-decl operand, avoiding a copy.