Cleanup foo.h headers and __config to work in C

llvm-svn: 252274
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 60506cbcd48a905950971f7211ceef1867aa25c8
diff --git a/include/setjmp.h b/include/setjmp.h
index ec4a5f6..464b4a5 100644
--- a/include/setjmp.h
+++ b/include/setjmp.h
@@ -34,8 +34,12 @@
 
 #include_next <setjmp.h>
 
+#ifdef __cplusplus
+
 #ifndef setjmp
 #define setjmp(env) setjmp(env)
 #endif
 
+#endif // __cplusplus
+
 #endif  // _LIBCPP_SETJMP_H