implement a missing feature in the #include handler, where

implement a missing feature in the #include handler, where
it did not handle <xyz> headers coming from macro expansions.
This requires special treatment, as the include name is lexed
as multiple tokens, which require reassembly before processing.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@40418 91177308-0d34-0410-b5e6-96231b3b80d8