ifcvt: Fix store flag of XImode on aarch64 while ifcvt [PR123294]

ifcvt: Fix store flag of XImode on aarch64 while ifcvt [PR123294]

In the testcase ifcvt is trying to do a emit_store_flag into a XImode.
That will cause an ICE because XImode does not have any arithmetic optabs
associated with it. This is because it is greater than MAX_FIXED_MODE_SIZE
(along other things).
noce_emit_store_flag already has code to reject non-scalar modes, so
this adds a new check for modes that are greater than MAX_FIXED_MODE_SIZE.

Bootstrapped and tested on aarch64-linux-gnu.

	PR rtl-optimization/123294

gcc/ChangeLog:

	* ifcvt.cc (noce_emit_store_flag): Reject modes
	greater than MAX_FIXED_MODE_SIZE.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr123294-1.c: New test.
	* gcc.target/aarch64/pr123294-1.c: New test.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>