MFC r269534:

  Integrate lib/libmp into the build/kyua

  - Remove the .t wrapper
  - Fix -Wreturn-type warnings with clang

  This change has been tested on amd64/i386

  Phabric: D530
  Reviewed by: jmmv
  Approved by: jmmv (co--mentor)
  MFC after: 2 weeks
  Sponsored by: EMC / Isilon Storage Division

MFC note: src.opts.mk in the original commit was changed to
          bsd.own.mk.
MFC r270116:

 Fix typo in lib/atf/libatfc++/Makefile

 LIBATFC should be LIBATF_C; this was missed in the initial import
 (r241823)

 PR: 192731
 MFC after: 3 days
 Phabric: D619
 Approved by: rpaulo (mentor)