[APFloat] Convert all references to fcNormal to references to isFiniteNonZero().

[APFloat] Convert all references to fcNormal to references to isFiniteNonZero().

Currently inside APFloat fcNormal still implies the old definition of Normal
(i.e. isFiniteNonZero) instead of the proper IEEE-754R definition that the
external method isNormal() uses.

This patch prepares for the internal switch inside APFloat by converting all
references that check if a category is fcNormal directly with an indirect call
via isFiniteNonZero().

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185036 91177308-0d34-0410-b5e6-96231b3b80d8