use the whole reg for return values

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@27116 3ad0048d-3df7-0310-abae-a5850022a9f2
support sign/zero extension to subreg sizes, not just always to 32bit

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@27117 3ad0048d-3df7-0310-abae-a5850022a9f2