test-includes: Add -ansi to the compile line to catch problems

We support C89 files, but compile everything in the tree with C99 or
newer. By compiling these -ansi, that will force C89 which doesn't
understand inline. All our header files must use __inline instead of
inline when they define inline functions.

Sponsored by: Netflix
Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D43235