16bit Thumb is not able to use tst with an immediate value

r28315 introduced an arm optimization which requires
  tst rX, #imm
to work. This is not available on 16bit thumb, I've disabled that
optimization on thumb for now.

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@28360 3ad0048d-3df7-0310-abae-a5850022a9f2