[ADT] Fix template parameter names of llvm::{upper|lower}_bound

Summary:
Rename template parameter for a search value from 'ForwardIt' to 'T'.
While here, also use perfect forwarding to pass the value to STL algos.

Reviewers: sammccall

Reviewed By: sammccall

Subscribers: dexonsmith, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60510

llvm-svn: 358158