libc: remove C++ comments from public headers.

Change-Id: I4af84f912062cd2ff34711c25122fb323f20c032
diff --git a/libc/include/pthread.h b/libc/include/pthread.h
index 9773dcb..99e747a 100644
--- a/libc/include/pthread.h
+++ b/libc/include/pthread.h
@@ -309,4 +309,4 @@
 #define LONG_LONG_MAX __LONG_LONG_MAX__
 #define LONG_LONG_MIN (-__LONG_LONG_MAX__ - 1)
 
-#endif // _PTHREAD_H_
+#endif /* _PTHREAD_H_ */