re PR tree-optimization/93210 (Sub-optimal code optimization on struct/combound const...

re PR tree-optimization/93210 (Sub-optimal code optimization on struct/combound constexpr (gcc vs. clang))

Regarding test gcc.dg/pr93210.c, on different targets GIMPLE code may
slightly differ which is why the scan-tree-dump-times directive may
fail.  For example, for a RETURN_EXPR on x86_64 we have

  return 0x11100f0e0d0c0a090807060504030201;

whereas on IBM Z the first operand is a RESULT_DECL like

  <retval> = 0x102030405060708090a0c0d0e0f1011;
  return <retval>;

gcc/testsuite/ChangeLog:

	* gcc.dg/pr93210.c: Adapt regex in order to also support a
	RESULT_DECL as an operand for a RETURN_EXPR.