Add testsuite/testsuite_string.h header to help testing __gnu_debug::basic_string like
std::basic_string depending on _GLIBCXX_DEBUG.

Add using of base type methods in __gnu_debug::basic_string to make use of the method
overloads when there is no debug version.

Fix _GLIBCXX_DEBUG_PEDANTIC assertions in <debug/string>. This header has to be used directly
like __gnu_debug::string, it is not included by _GLIBCXX_DEBUG. It means that
_GLIBCXX_DEBUG_PEDANTIC is not considered to define __glibcxx_check_string and
__glibcxx_check_string_len which are then empty macros. Now those macros are defined
directly in <debug/string> and properly consider _GLIBCXX_DEBUG_PEDANTIC.

libstdc++-v3/ChangeLog:

	* include/debug/debug.h [_GLIBCXX_DEBUG](__glibcxx_requires_string): Define
	using _GLIBCXX_DEBUG_PEDASSERT.
	[_GLIBCXX_DEBUG](__glibcxx_requires_string_len): Likewise.
	* include/debug/macros.h
	(__glibcxx_check_string, __glibcxx_check_string_len): Move...
	* include/debug/string
	(__glibcxx_check_string, __glibcxx_check_string_len): ...here. And define depending
	on _GLIBCXX_DEBUG_PEDANTIC no matter if _GLIBCXX_DEBUG is defined.
	Add using of std::string find, rfind, find_first_of, find_last_of, find_first_not_of
	and find_last_not_of. Remove debug implementations having no debug assertion.
	* testsuite/util/testsuite_string.h: New file. Provides __gnu_test::string and
	__gnu_test::wtring which definition depends on _GLIBCXX_DEBUG.
	* testsuite/21_strings/basic_string/debug/find1_neg.cc: New test case.
	* testsuite/21_strings/basic_string/debug/find2_neg.cc: New test case.
	* testsuite/21_strings/basic_string/operations/find/char/1.cc:
	Include <testsuite_string.h> and use __gnu_test::string.
	* testsuite/21_strings/basic_string/operations/find/char/2.cc: Likewise.
	* testsuite/21_strings/basic_string/operations/find/char/3.cc: Likewise.
	* testsuite/21_strings/basic_string/operations/find/char/4.cc: Likewise.
	* testsuite/21_strings/basic_string/operations/find/char/5.cc: Likewise.
	* testsuite/21_strings/basic_string/operations/find/char/6.cc: Likewise.
	* testsuite/21_strings/basic_string/operations/find/wchar_t/1.cc:
	Include <testsuite_string.h> and use __gnu_test::wstring.
	* testsuite/21_strings/basic_string/operations/find/wchar_t/2.cc: Likewise.
	* testsuite/21_strings/basic_string/operations/find/wchar_t/3.cc: Likewise.
	* testsuite/21_strings/basic_string/operations/find/wchar_t/4.cc: Likewise.
	* testsuite/21_strings/basic_string/operations/find/wchar_t/5.cc: Likewise.
	* testsuite/21_strings/basic_string/operations/find/wchar_t/6.cc: Likewise.

From-SVN: r279813

From-SVN: r267494

2018-07-06  François Dumont  <fdumont@gcc.gnu.org>

	* include/debug/functions.h (__gnu_debug::__check_string): Move...
	* include/debug/string (__gnu_debug::__check_string): ... here.
	(_GLIBCXX_DEBUG_VERIFY_STR_COND_AT): New.
	(__glibcxx_check_string_n_constructor): New.
	(__gnu_debug::basic_string<>(const _CharT*, size_type, const _Alloc&)):
	Use latter.
	(__glibcxx_check_string_constructor): New.
	(__gnu_debug::basic_string<>(const _CharT*, const _Alloc&)):
	Use latter.
	* testsuite/21_strings/basic_string/debug/1_neg.cc: New.
	* testsuite/21_strings/basic_string/debug/2_neg.cc: New.

From-SVN: r262480