[PATCH] Allow encoded 8-bit floating point constants in ARM vmov instructions

[David Peixotto]

> Why do we want fconstf/fconstd aliases? Those are pre-unified syntax
> instructions, which we're trying to remove from LLVM, not add.

Mainly because I see these instructions still appearing in code and gcc
accepts them.  We already support a number of aliases for pre-unified syntax
(e.g. flds, fldd). I count at least 40 in lib/Target/ARM/ARMInstrVFP.td. 

Is there a reason not to support them? I think they maps fairly cleanly to
the vmov.f32/vmov.f64 instructions.