This enables use of the 'S' constraint for inline ASM operands on SystemZ, which allows for a memory reference with a signed 20-bit immediate displacement. This patch includes corresponding documentation and test case updates.
I've changed the 'T' constraint to match the new behavior for 'S', as 'T' also uses a long displacement (though index constraints are still not implemented). I also changed 'm' to match the behavior for 'S' as this will allow for a wider range of displacements for 'm', though correct me if that's not the right decision.