The builds were failing under Xcode 10 because of the new build system.
Even when reverted to the old build system, the build was failing
on the analyzer and swift bridging header, so it seems the general
logic for searching for things was changed in a way the setting does
not always cover.

- Disable HeaderMaps.
- Set user header search paths instead of system search paths.
- Turn off always search user paths (now recommended).

Tested in Xcode 10.1 and 9.4.1; both are able to build/pass with this.