tree-optimization/114197 - unexpected if-conversion for vectorization

tree-optimization/114197 - unexpected if-conversion for vectorization

The following avoids lowering a volatile bitfiled access and in case
the if-converted and original loops end up in different outer loops
because of simplifcations enabled scrap the result since that is not
how the vectorizer expects the loops to be laid out.

	PR tree-optimization/114197
	* tree-if-conv.cc (bitfields_to_lower_p): Do not lower if
	there are volatile bitfield accesses.
	(pass_if_conversion::execute): Throw away result if the
	if-converted and original loops are not nested as expected.

	* gcc.dg/torture/pr114197.c: New testcase.