IRBuilder: Remove redundant check around SetInstDebugLocation call.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173591 91177308-0d34-0410-b5e6-96231b3b80d8
PR14566: Debug Info: Removing top level lexical blocks

This adds support for LLVM to accept metadata that doesn't include a top level
lexical block in a function. Specifically LLVM couldn't handle this when there
were file changes relating to these blocks. I've updated a few test cases to
ensure other functionality (such as inlining) isn't affected by this change, but
haven't pervasively updated all the test cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173592 91177308-0d34-0410-b5e6-96231b3b80d8