ARM target does not use printAliasInstr machinery which

forces having special checks in ArmInstPrinter::printInstruction. This
patch addresses this issue.

Not all special checks could be removed: either they involve elaborated
conditions under which the alias is emitted (e.g. ldm/stm on sp may be
pop/push but only if the number of registers is >= 2) or the number
of registers is multivalued (like happens again with ldm/stm) and they
do not match the InstAlias pattern which assumes single-valued operands
in the pattern.

Patch by: Roger Ferrer Ibanez

Differential Revision: http://reviews.llvm.org/D20237

llvm-svn: 271667