fix windows build

kstyle/CMakeLists.txt

@@ -126,6 +126,12 @@ else()
   add_library(breeze MODULE ${breeze_PART_SRCS})
   target_link_libraries(breeze Qt5::Core Qt5::Gui Qt5::Widgets Qt5::DBus)
   target_link_libraries(breeze KF5::ConfigCore KF5::ConfigWidgets KF5::GuiAddons KF5::Style KF5::WindowSystem)
+  
+  if (WIN32)
+    # As stated in http://msdn.microsoft.com/en-us/library/4hwaceh6.aspx M_PI only gets defined
+    # when if _USE_MATH_DEFINES is defined
+    target_compile_definitions(breeze PRIVATE _USE_MATH_DEFINES _BSD_SOURCE)
+    endif()
 
   if(XCB_XCB_FOUND)
     target_link_libraries(breeze ${XCB_LIBRARIES})