[LV] Merge floating-point and integer induction widening code

[LV] Merge floating-point and integer induction widening code

This patch merges the existing floating-point induction variable widening code
into the integer induction variable widening code, creating a single set of
functions for both kinds of inductions. The primary motivation for doing this
is to enable vector phi node creation for floating-point induction variables.

Differential Revision: https://reviews.llvm.org/D30211

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296145 91177308-0d34-0410-b5e6-96231b3b80d8