Summary:
Builds fail because libxml/xmlreader.h isn't found. Adding the include
directory to the include list fixes the issue. This is what we already do on
non-macOS platforms in the same file.
Reviewers: clayborg, xiaobai, lanza
Reviewed By: clayborg, lanza
Subscribers: mgorny
Differential Revision: https://reviews.llvm.org/D50918
llvm-svn: 340460