PR libstdc++/77356
	* include/bits/regex_compiler.tcc(_M_insert_bracket_matcher,
	_M_expression_term): Modify to support dash literal.
	* include/bits/regex_scanner.h: Add dash as a token type to make
	a different from the mandated dash literal by escaping.
	* include/bits/regex_scanner.tcc(_M_scan_in_bracket): Emit dash
	token in bracket expression parsing.
	* testsuite/28_regex/regression.cc: Add new testcases.

From-SVN: r239794