rtl: remove unused variables

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@23275 3ad0048d-3df7-0310-abae-a5850022a9f2
+ redirect calls to empty virtual methods to FPC_EMPTYMETHOD
* do empty subroutine/method optimization only for O2 and higer

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@23276 3ad0048d-3df7-0310-abae-a5850022a9f2