fix windows build

kstyle/CMakeLists.txt

@@ -127,6 +127,12 @@ else()
   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})
     target_link_libraries(breeze Qt5::X11Extras)