[APInt] Use MathExtras.h BitsToFloat/Double and Float/DoubleToBits instead of type punning through a union

The functions in MathExtras.h uses a safer memcpy instead of going through a union.

Differential Revision: https://reviews.llvm.org/D33116

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@302916 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed