libstdc++: Add dg-timeout-factor to some more regex tests

I'm seeing these fail with tool_timeout=30 on a busy machine.

libstdc++-v3/ChangeLog:

	* testsuite/28_regex/algorithms/regex_replace/char/103664.cc:
	Add dg-timeout-factor directive.
	* testsuite/28_regex/basic_regex/84110.cc: Likewise.
	* testsuite/28_regex/basic_regex/ctors/char/other.cc: Likewise.
	* testsuite/28_regex/match_results/102667.cc: Likewise.