lightly used. Find the proper .m file when we depend on *_if.[ch] in
the srcs line, with seat-belts for false positive matches. This uses
make's path mechanism. A further refinement would be to calculate this
once, and then pass the resulting _MPATH to modules submakes.
Differential Revision: https://reviews.freebsd.org/D2327
driver for CAM ATA subsystem. This driver supports same hardware as
atamarvell, ataadaptec and atamvsata drivers from ata(4), but provides
many additional features, such as NCQ, PMP, etc.