[PATCH] PR libstdc++/85729 add linkage specifications to headers

[Jonathan Wakely]

This works around user error where our headers get included within an
extern "C" block.

        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.

Tested powerpc64le-linux, committed to trunk.



commit 72a9c99cc1fc94c6b4c1fbe2ae223d07237a817e
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Thu May 10 12:50:55 2018 +0100

    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.

diff --git a/libstdc++-v3/include/bits/c++config 
b/libstdc++-v3/include/bits/c++config
index bfe268da825..280f65e1ba0 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/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)
   {
diff --git a/libstdc++-v3/include/bits/std_abs.h 
b/libstdc++-v3/include/bits/std_abs.h
index 6e4551d6597..bcea4f49203 100644
--- a/libstdc++-v3/include/bits/std_abs.h
+++ b/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
diff --git a/libstdc++-v3/include/c_global/cstddef 
b/libstdc++-v3/include/c_global/cstddef
index 36d7d716cc3..0ca3b82338a 100644
--- a/libstdc++-v3/include/c_global/cstddef
+++ b/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
diff --git a/libstdc++-v3/include/c_global/cstring 
b/libstdc++-v3/include/c_global/cstring
index 399f41fb164..2bca01b7f08 100644
--- a/libstdc++-v3/include/c_global/cstring
+++ b/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
diff --git a/libstdc++-v3/include/c_global/cwchar 
b/libstdc++-v3/include/c_global/cwchar
index 475322ee806..7557c7768aa 100644
--- a/libstdc++-v3/include/c_global/cwchar
+++ b/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