PR libstdc++/85729 add linkage specifications to headers

	PR libstdc++/85729
	* include/bits/c++config.h (__replacement_assert): Add linkage
	specification.
	* include/bits/std_abs.h: Add comment to closing brace of block.
	* include/c_global/cstddef: Add linkage specification.
	* include/c_global/cstring: Likewise.
	* include/c_global/cwchar: Likewise.

From-SVN: r260114

libstdc++-v3/ChangeLog

+2018-05-10  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/85729
+	* include/bits/c++config.h (__replacement_assert): Add linkage
+	specification.
+	* include/bits/std_abs.h: Add comment to closing brace of block.
+	* include/c_global/cstddef: Add linkage specification.
+	* include/c_global/cstring: Likewise.
+	* include/c_global/cwchar: Likewise.
+
 2018-05-09  François Dumont  <fdumont@gcc.gnu.org>
 
 	* include/debug/safe_iterator.h (_Safe_iterator<>::_M_constant()):

libstdc++-v3/include/bits/c++config

@@ -438,7 +438,7 @@ namespace std
 {
   // Avoid the use of assert, because we're trying to keep the <cassert>
   // include out of the mix.
-  inline void
+  extern "C++" inline void
   __replacement_assert(const char* __file, int __line,
 		       const char* __function, const char* __condition)
   {

libstdc++-v3/include/bits/std_abs.h

@@ -105,6 +105,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
-}
+} // extern "C"++"
 
 #endif // _GLIBCXX_BITS_STD_ABS_H

libstdc++-v3/include/c_global/cstddef

@@ -49,13 +49,15 @@
 #include <bits/c++config.h>
 #include <stddef.h>
 
+extern "C++"
+{
 #if __cplusplus >= 201103L
 namespace std
 {
   // We handle size_t, ptrdiff_t, and nullptr_t in c++config.h.
   using ::max_align_t;
 }
-#endif
+#endif // C++11
 
 #if __cplusplus >= 201703L
 namespace std
@@ -186,6 +188,7 @@ namespace std
     { return _IntegerType(__b); }
 
 } // namespace std
-#endif
+#endif // C++17
+} // extern "C++"
 
 #endif // _GLIBCXX_CSTDDEF

libstdc++-v3/include/c_global/cstring

@@ -68,6 +68,8 @@
 #undef strtok
 #undef strxfrm
 
+extern "C++"
+{
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
@@ -119,5 +121,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
+} // extern "C++"
 
 #endif

libstdc++-v3/include/c_global/cwchar

@@ -132,6 +132,8 @@ namespace std
 
 #if _GLIBCXX_USE_WCHAR_T
 
+extern "C++"
+{
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
@@ -231,6 +233,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
+} // extern "C++"
 
 #if _GLIBCXX_USE_C99_WCHAR