Fix fptosi, fptoui from f16 vectors to i8, i16 vectors

Summary:
Convert f16 vectors to corresponding f32 vectors before doing the
conversion to int.

Add tests for v4f16, v8f16.

Reviewers: ab, jmolloy

Subscribers: llvm-commits, srhines

Differential Revision: http://reviews.llvm.org/D14936

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255263 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed