runtime: use explicit name for placement new

The android build seems to find a conflict in the overload set for the
placement new operator due to the custom new overload.  Provide the
indicator that we want the placement new allocator by using the
explicitly namespaced spelling.

Thanks to @buttaface for reporting the build failure.

(cherry picked from commit ce6d97d)

Author: compnerd

stdlib/public/runtime/MetadataImpl.h

@@ -100,11 +100,11 @@ struct NativeBox {
   }
 
   static T *initializeWithCopy(T *dest, T *src) {
-    return new (dest) T(*src);
+    return ::new (dest) T(*src);
   }
 
   static T *initializeWithTake(T *dest, T *src) {
-    T *result = new (dest) T(std::move(*src));
+    T *result = ::new (dest) T(std::move(*src));
     src->T::~T();
     return result;
   }