Raise WARNS from 1 to 6 (the default)
Fix warnings:
* Use C99 designated initializers for structs, and initialize all fields
* Mark global variables as static
* Mark unused function arguments
* Be careful about signed/unsigned comparisons
Reviewed by: eadler
MFC after: 4 weeks
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D5328
a107331a23