These functions can't be noexcept because the iterators stored in the
sub_match objects can throw on any operation.

libstdc++-v3/ChangeLog:

	PR libstdc++/94627
	* include/bits/regex.h (operator==, operator!=): Remove noexcept
	equality comparisons for match_results.
	* testsuite/28_regex/match_results/94627.cc: New test.

(cherry picked from commit a1a0dc4548979f8a340a7ea71624a52a20e1e0b3)