wxOSX compilation fix after the last commit.

Add the missing wx/time.h header required for using wxGetLocalTimeMillis().

Also add WXUNUSED() around the unused parameters of DrawGauge().

See #16406.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77024 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775