The ARM NEON vector compare instructions take three arguments. However, the

assembler should also accept a two arg form, as the docuemntation specifies that
the first (destination) register is optional.

This patch uses TwoOperandAliasConstraint to add the two argument form.

It also fixes an 80-column formatting problem in:
  test/MC/ARM/neon-bitwise-encoding

<rdar://problem/12909419> Clang rejects ARM NEON assembly instructions

llvm-svn: 175221