PR libstdc++/85098 add missing definitions for static constants

PR libstdc++/85098 add missing definitions for static constants

In C++11 and C++14 any odr-use of these constants requires a definition
at namespace-scope.  In C++17 they are implicitly inline and so the
namespace-scope redeclarations are redundant (and allowing them is
deprecated).

Backport from mainline
2018-05-18  Jonathan Wakely  <jwakely@redhat.com>

	PR libstdc++/85098
	* include/bits/regex.h [__cplusplus < 201703L] (basic_regex::icase)
	(basic_regex::nosubs, basic_regex::optimize, basic_regex::collate)
	(basic_regex::ECMAScript, basic_regex::basic, basic_regex::extended)
	(basic_regex::awk, basic_regex::grep, basic_regex::egrep): Add
	definitions.
	* include/bits/regex_automaton.h (_NFA::_M_insert_state): Adjust
	whitespace.
	* testsuite/28_regex/basic_regex/85098.cc: New

From-SVN: r265083