util/RefCount, db/simple/Mount: remove obsolete libc++ workarounds

No longer a problem with NDK r16.

src/db/plugins/simple/Mount.cxx

@@ -25,13 +25,6 @@
 #include "db/Interface.hxx"
 #include "fs/Traits.hxx"
 
-#ifdef _LIBCPP_VERSION
-/* workaround for "error: incomplete type 'PlaylistInfo' used in type
-   trait expression" with libc++ version 3900 (from Android NDK
-   r13b) */
-#include "db/PlaylistInfo.hxx"
-#endif
-
 #include <string>
 
 struct PrefixedLightDirectory : LightDirectory {

src/util/RefCount.hxx

@@ -42,11 +42,6 @@ class RefCount {
 	std::atomic_uint n;
 
 public:
-#ifndef _LIBCPP_VERSION
-	/* the "constexpr" is missing in libc++'s "atomic"
-	   implementation */
-	constexpr
-#endif
 	RefCount():n(1) {}
 
 	void Increment() {