X86: Use the constant area for more operations.

Allow FP HNeg to use the constant area to hold the constant to flip the
sign bit.

Enhance some math intrinsics to allow the use of the constant
area: Abs{Float,Double}, {Min,Max}{FloatFloat,DoubleDouble}.

Allow compares of floats/doubles to constants using the constant area.

These eliminate almost all uses of loading constants from the stack.

Change-Id: Ic4b831565825cbe9f0801b1b53c1013be7c87ae4
Signed-off-by: Mark Mendell <mark.p.mendell@intel.com>