make cxxabi.h safe for C code to include

llvm-svn: 136682
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 2dfc79b19ef57db6ac6bdf46dfdd3508ac712e91
diff --git a/include/cxxabi.h b/include/cxxabi.h
index 196e230..933ff21 100644
--- a/include/cxxabi.h
+++ b/include/cxxabi.h
@@ -20,6 +20,9 @@
 
 #define LIBCXXABI_NORETURN  __attribute__((noreturn))
 
+
+#ifdef __cplusplus
+
 namespace std {
     class type_info; // forward declaration
 }
@@ -183,6 +186,7 @@
   } // extern "C"
 } // namespace __cxxabiv1
 
+#endif // __cplusplus
 
 
 #endif // __CXXABI_H