MFC various fixes to the tools/regression/ tests.

- r262953 Fix m4 tests so that they run cleanly with prove.
- r262954 Fix printf tests so that they run cleanly with prove.
- r262959 Fix sed tests so that they run cleanly with prove.
- r262960 Fix yacc tests so that they run cleanly with prove.
- r262961 Fix pkill tests so that they run cleanly with prove.
- r262962 Fix ncal tests so that they run cleanly with prove.
- r263081 Fix lastcomm tests under amd64.
- r263082 Only run the make tests when make is fmake.
- r263083 Fix sa tests.
- r263084 Turn a test precondition into a skip in the mdconfig tests.
- r263085 Make the strerror tests work without libtap.
- r263087 Remove broken tests for eui64_line.
- r263221 Change etcupdate tests to return 1 on test failures.
- r263352 Make the priv test program exit with non-zero if any failures are detected.
- r263353 errx prepends the program name to the message; don't do it by hand.
- r263362 Include strings.h so that bpf_filter.c can be built in userland.