Fix MinGW build breakage


git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@4282 3789f03b-4d11-0410-bbf8-ca57d06f2519
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9d5bff7..1447eba 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -110,6 +110,8 @@
 add_definitions(-DHAVE_CONFIG_H)
 include_directories(${CMAKE_BINARY_DIR})
 
+add_definitions(-D_WIN32_IE=0x0500 -D_WIN32_WINNT=0x0500)
+
 add_subdirectory(common)
 add_subdirectory(win)