Add xfail-if to some tests that fail with COW strings

These tests fail when run with -D_GLIBCXX_USE_CXX11_ABI=0

	* testsuite/21_strings/basic_string/cons/char/deduction.cc: XFAIL for
	COW strings.
	* testsuite/21_strings/basic_string/cons/wchar_t/deduction.cc:
	Likewise.
	* testsuite/21_strings/basic_string/requirements/
	explicit_instantiation/debug.cc: Likewise.

From-SVN: r262448

libstdc++-v3/ChangeLog

 2018-07-05  Jonathan Wakely  <jwakely@redhat.com>
 
+	* testsuite/21_strings/basic_string/cons/char/deduction.cc: XFAIL for
+	COW strings.
+	* testsuite/21_strings/basic_string/cons/wchar_t/deduction.cc:
+	Likewise.
+	* testsuite/21_strings/basic_string/requirements/
+	explicit_instantiation/debug.cc: Likewise.
+
 	PR libstdc++/58265
 	* include/bits/basic_string.h [!_GLIBCXX_USE_CXX11_ABI]
 	(basic_string::assign(basic_string&&)): Add conditional noexcept

libstdc++-v3/testsuite/21_strings/basic_string/cons/char/deduction.cc

@@ -17,6 +17,7 @@
 
 // { dg-options "-std=gnu++17" }
 // { dg-do compile { target c++17 } }
+// { dg-xfail-if "COW string missing deduction guides" { ! cxx11-abi } }
 
 #include <string>
 #include <testsuite_iterators.h>

libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/deduction.cc

@@ -17,6 +17,7 @@
 
 // { dg-options "-std=gnu++17" }
 // { dg-do compile { target c++17 } }
+// { dg-xfail-if "COW string missing deduction guides" { ! cxx11-abi } }
 
 #include <string>
 #include <testsuite_iterators.h>

libstdc++-v3/testsuite/21_strings/basic_string/requirements/explicit_instantiation/debug.cc

@@ -20,8 +20,9 @@
 #include <debug/string>
 
 // { dg-do compile }
+// { dg-xfail-if "COW string missing some required members" { ! cxx11-abi } }
 
 // libstdc++/21770
 namespace debug = __gnu_debug;
-template class debug::basic_string<int, std::char_traits<int>, 
+template class debug::basic_string<int, std::char_traits<int>,
 				   std::allocator<char> >;