Fixes a coalescer bug that caused llc to crash on 2009-11-30-LiveVariablesBug.ll

with the fix in 103157.

%reg1039:1<def> = VMOVS %S1<kill>, pred:14, pred:%reg0
is not coalescable since none of the super-registers of S1 are in reg1039's
register class: DPR_VFP2. But it is still a legal copy instruction so it should
not assert.

llvm-svn: 103170