[libc++] Explicit return in non-void function

[bogden]

Summary

This test contains a non-void function with no explicit return,
causing it to fail when built with -Werror=return-type. This patch adds
a return to the function.

[bogden]

I think this fix is OK, but I'm not clear on why we need both C and D, so perhaps it is important that the function does not have a return statement.

[mclow.lists]

LGTM.

C and D are different failure modes for uses_allocator, since the standard says that it has to be a nested type.

[Eugene.Zelenko]

Committed in r269298.

test/std/utilities/memory/allocator.uses/allocator.uses.trait/uses_allocator.pass.cpp

struct B
     typedef int allocator_type;
 };
 
 struct C {
   static int allocator_type;
 };
 
 struct D {
-  static int allocator_type() {}
+  static int allocator_type() { return 0; }
 };
 
 struct E {
 private:
   typedef int allocator_type;
 };
 
 int main()