Use correct wxDEBUG_LEVEL value when building wxscintilla library.

wxScintilla code uses wxVector<> which brings in wxDEBUG_LEVEL-dependent code
so we must use the wxDEBUG_LEVEL value consistent with the rest of the library
when building it.

Simply pass wxDEBUG_LEVEL definition on the compiler command line if it's
different from the default.

Closes #12626.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66223 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775