Reference the test case "packs" to fix warnings

Put the various atf_tc_pack_t variables generated by ATF_TC to use in
the macros_h_test.c file so that we prevent some build warnings (and
thus some build errors) with clang and -Wunused.

Obtained from:  atf (git 70126d013db25c72539803f19f7e00baddacdf51)


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271875 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f