[analyzer] Don't run unreachable code checker on inlined functions.

This is still an alpha checker, but we use it in certain tests to make sure
something is not being executed.

This should fix the buildbots.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188682 91177308-0d34-0410-b5e6-96231b3b80d8