Though the previous xform applies to literally dozens (hundreds?) of variables

in SPEC, the subsequent optimziations that we are after don't play with
with FP values, so disable this xform for them.  Really we just don't want
stuff like:

double G;   (always 0 or 412312.312)
  = G;

turning into:

bool G_b;
  = G_b ? 412312.312 : 0;

We'd rather just do the load.

-Chris

llvm-svn: 18819