don't shadow functions with macros in C++

C++ programmers typically expect something like "::function(x,y)" to work
and may be surprised to find that "(::function)(x,y)" is actually required
due to the headers declaring a macro version of some standard functions.

We already omit function-like macros for C++ in most cases where there is
a real function available. This commit extends this to the remaining
function-like macros which have a real function version.

include/threads.h

@@ -51,7 +51,9 @@ void thrd_yield(void);
 
 thrd_t thrd_current(void);
 int thrd_equal(thrd_t, thrd_t);
+#ifndef __cplusplus
 #define thrd_equal(A, B) ((A) == (B))
+#endif
 
 void call_once(once_flag *, void (*)(void));