tree-optimization/110496 - TYPE_PRECISION issue with store-merging

tree-optimization/110496 - TYPE_PRECISION issue with store-merging

When store-merging looks for bswap opportunities we also handle
BIT_FIELD_REFs where we verify the refed object is of scalar
type but we don't check for the result type we eventually use.
That's done later but after we eventually query TYPE_PRECISION.
The following re-orders this.

	PR tree-optimization/110496
	* gimple-ssa-store-merging.cc (find_bswap_or_nop_1): Re-order
	verifying and TYPE_PRECISION query for the BIT_FIELD_REF case.

	* gcc.dg/pr110496.c: New testcase.