APFloat: Use isDenormal instead of hand-rolled code to check for denormals.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183072 91177308-0d34-0410-b5e6-96231b3b80d8
APInt: Simplify code. No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183073 91177308-0d34-0410-b5e6-96231b3b80d8