Adjust linker flags for static build with cmake/mingw-w64

It is not clear anymore where I picked that change up and for
what reason. Never touch a running system so let's keep it.

Change-Id: Iad665f18da5b4540f0899829a0165e1d3aa4ea60

src/corelib/Qt5CoreConfigExtras.cmake.in

@@ -206,3 +206,9 @@ if(NOT \"${QT_NO_CREATE_VERSIONLESS_TARGETS}\" AND NOT TARGET Qt::WinMain)
     )
 endif()
 !!ENDIF
+
+!!IF !isEmpty(CMAKE_STATIC_WINDOWS_BUILD)
+set(_isExe $<STREQUAL:$<TARGET_PROPERTY:TYPE>,EXECUTABLE>)
+# INTERFACE_LINK_LIBRARIES is used to pass a linker flag '-static' and library ws2_32
+set_target_properties(${IMPORTED_TARGET_NAME} PROPERTIES \"INTERFACE_LINK_LIBRARIES\" \"$<${_isExe}:-static;ws2_32>\")
+unset(_isExe)