[Intrinsics] Merge lround.i32 and lround.i64 into a single intrinsic with overloaded...

[Intrinsics] Merge lround.i32 and lround.i64 into a single intrinsic with overloaded result type. Make result type for llvm.llround overloaded instead of fixing to i64

We shouldn't really make assumptions about possible sizes for long and long long. And longer term we should probably support vectorizing these intrinsics. By making the result types not fixed we can support vectors as well.

Differential Revision: https://reviews.llvm.org/D62026

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@361169 91177308-0d34-0410-b5e6-96231b3b80d8