Use this instead of manually copying LR to PC. With GNU libunwind,
both registers are equal after unw_step.

With the LLVM libunwind (which Apple uses), the return address isn't
reflected at all in LR, only in UNW_REG_IP.
Signed-off-by: Martin Storsjo <martin@martin.st>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>