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/errno.h b/include/errno.h
index 556ef61..ee64291 100644
--- a/include/errno.h
+++ b/include/errno.h
@@ -31,6 +31,8 @@
 
 #include_next <errno.h>
 
+#ifdef __cplusplus
+
 #if !defined(EOWNERDEAD) || !defined(ENOTRECOVERABLE)
 
 #ifdef ELAST
@@ -391,4 +393,6 @@
 #define EMLINK 9979
 #endif
 
+#endif // __cplusplus
+
 #endif  // _LIBCPP_ERRNO_H