add winrt patch

Author: zilongshanren

contrib/src/png/winrt.patch

@@ -0,0 +1,14 @@
+--- png/pngpriv.h.orig	2013-05-09 15:17:34.933583625 +0200
++++ png/pngpriv.h	2013-05-09 15:18:33.981581142 +0200
+@@ -360,11 +360,7 @@
+ 
+ /* Memory model/platform independent fns */
+ #ifndef PNG_ABORT
+-#  ifdef _WINDOWS_
+-#    define PNG_ABORT() ExitProcess(0)
+-#  else
+ #    define PNG_ABORT() abort()
+-#  endif
+ #endif
+ 
+ #ifdef USE_FAR_KEYWORD