Fix experimental::pmr typedefs and add tests

Fix experimental::pmr typedefs and add tests

The typedefs in <experimental/regex> and <experimental/string> don't
need to be in the __cxx11 namespace, because they are only aliases and
so will have the same mangled name as the underlying types.

Backport from mainline
2018-08-23  Jonathan Wakely  <jwakely@redhat.com>

	* testsuite/21_strings/basic_string/init-list.cc:
	Require cxx11-abi.
	* testsuite/experimental/polymorphic_allocator/pmr_typedefs_match.cc:
	Likewise.
	* testsuite/experimental/polymorphic_allocator/pmr_typedefs_string.cc:
	Likewise.

Backport from mainline
2018-08-22  Jonathan Wakely  <jwakely@redhat.com>

	PR libstdc++/87061
	* include/experimental/regex [!_GLIBCXX_USE_CXX11_ABI]
	(experimental::pmr::match_results, experimental::pmr::cmatch)
	(experimental::pmr::smatch, experimental::pmr::wcmatch)
	(experimental::pmr::wsmatch): Do not declare for gcc4-compatible ABI,
	because COW strings don't support C++11 allocator model.
	* include/experimental/string [!_GLIBCXX_USE_CXX11_ABI]
	(experimental::pmr::basic_string, experimental::pmr::string)
	(experimental::pmr::u16string, experimental::pmr::u32string)
	(experimental::pmr::wstring): Likewise.

Backport from mainline
2018-08-15  Jonathan Wakely  <jwakely@redhat.com>

	* include/experimental/regex: Remove begin/end macros for namespace.
	* include/experimental/string: Likewise.
	* testsuite/experimental/polymorphic_allocator/pmr_typedefs_deque.cc:
	New test.
	* testsuite/experimental/polymorphic_allocator/
	pmr_typedefs_forward_list.cc: New test.
	* testsuite/experimental/polymorphic_allocator/pmr_typedefs_list.cc:
	New test.
	* testsuite/experimental/polymorphic_allocator/pmr_typedefs_map.cc:
	New test.
	* testsuite/experimental/polymorphic_allocator/pmr_typedefs_match.cc:
	New test.
	* testsuite/experimental/polymorphic_allocator/
	pmr_typedefs_multimap.cc: New test.
	* testsuite/experimental/polymorphic_allocator/
	pmr_typedefs_multiset.cc: New test.
	* testsuite/experimental/polymorphic_allocator/pmr_typedefs_set.cc:
	New test.
	* testsuite/experimental/polymorphic_allocator/pmr_typedefs_string.cc:
	New test.
	* testsuite/experimental/polymorphic_allocator/
	pmr_typedefs_unordered_map.cc: New test.
	* testsuite/experimental/polymorphic_allocator/
	pmr_typedefs_unordered_multimap.cc: New test.
	* testsuite/experimental/polymorphic_allocator/
	pmr_typedefs_unordered_multiset.cc: New test.
	* testsuite/experimental/polymorphic_allocator/
	pmr_typedefs_unordered_set.cc: New test.
	* testsuite/experimental/polymorphic_allocator/pmr_typedefs_vector.cc:
	New test.

From-SVN: r265093