Enabled build with LLVM libc++ for Android.

modules/core/include/opencv2/core/operations.hpp

@@ -46,9 +46,9 @@
 #ifndef SKIP_INCLUDES
   #include <string.h>
   #include <limits.h>
+  #include <stddef.h>
 #endif // SKIP_INCLUDES
 
-
 #ifdef __cplusplus
 
 /////// exchange-add operation for atomic operations on reference counters ///////
@@ -66,7 +66,7 @@
 
     #if !(defined WIN32 || defined _WIN32) && (defined __i486__ || defined __i586__ || \
         defined __i686__ || defined __MMX__ || defined __SSE__  || defined __ppc__) || \
-        (defined __GNUC__ && defined _STLPORT_MAJOR) || \
+        defined _STLPORT_MAJOR || defined _LIBCPP_VERSION || \
         defined __EMSCRIPTEN__
 
       #define CV_XADD __sync_fetch_and_add