Demo project for #1918.
Work on a fork, which is based on Uber fork.
Change .buckfork to mgrebenets and .buckversion to 07e7e1b69e and turn ./buckw test mylib.
Result: works as expected.
Change .buckfork to facebook and .buckversion to 6c2f9a and try ./buckw test mylib again.
Result: fails to import "MyLibPrivate.h"