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