[x265] [PATCH 6 of 7] threadpool.cpp: ensure for minimum window version -> _WIN32_WINNT_WIN7

[praveen at multicorewareinc.com]

# HG changeset patch
# User Praveen Tiwari <praveen at multicorewareinc.com>
# Date 1463739280 -19800
#      Fri May 20 15:44:40 2016 +0530
# Node ID 521874f0eea07c26b6a9580302fe61fc7f223e02
# Parent  e96bb0aaec630d44ea318222ae221fe116f4f11a
threadpool.cpp: ensure for minimum window version -> _WIN32_WINNT_WIN7

diff -r e96bb0aaec63 -r 521874f0eea0 source/common/threadpool.cpp
--- a/source/common/threadpool.cpp	Fri May 20 15:35:37 2016 +0530
+++ b/source/common/threadpool.cpp	Fri May 20 15:44:40 2016 +0530
@@ -28,9 +28,9 @@
 
 #include <new>
 
-#if _WIN32
+#if defined(_WIN32_WINNT) && _WIN32_WINNT >= _WIN32_WINNT_WIN7
 #include <winnt.h>
-#endif // _WIN32
+#endif
 
 #if X86_64