Correctly support assembling "pushw $imm8" on x86-64 targets.
Also some cleanup of the PUSH instructions (PUSH64i16 and PUSHi16 actually
represent the same instruction)
This fixes PR23996
Patch by: david.l.kreitzer@intel.com
Differential Revision: http://reviews.llvm.org/D10878
llvm-svn: 241404
Michael Kuperstein