* tests/mktests.sh: Only skip internal macros starting with

* tests/mktests.sh: Only skip internal macros starting with
`_AC_' or `__AC_'.  Noted by Stepan Kasal.
Update exclusion lists for the test suite to this end:
(AC_ARG_VAR): Do test this now.
(AC_REPLACE_FUNCS): This needs an argument.
(AC_LINKER_OPTION): Remove (renamed to _AC_LINKER_OPTION).
(AC_LIST_MEMBER_OF): Likewise (renamed to _AC_LIST_MEMBER_IF).
(AC_LINK_FILES): Obsoleted since (and thus AU_DEFUN'ed).