coverage: expose a bug in aclocal (spurious warnings)

coverage: expose a bug in aclocal (spurious warnings)

When some macro expanded in configure.ac calls AC_REQUIRE on another
macro that is defined in one of the local m4 macro dirs specified
with one of the macros AC_CONFIG_MACRO_DIRS or AC_CONFIG_MACRO_DIR,
aclocal prints spurious warnings like:

    configure.ac:4: warning: MY_BAR is m4_require'd but not m4_defun'd
    configure.ac:3: MY_FOO is expanded from...

Expose this weakness in our testsuite.

Reported by Nick Bowler; see point (4) of:
<http://lists.gnu.org/archive/html/autoconf-patches/2012-11/msg00000.html>

* t/aclocal-macrodir.tap ("AC_CONFIG_MACRO_DIR interaction with
AC_REQUIRE"): New test, still xfailing.
* t/aclocal-macrodirs.tap ("AC_CONFIG_MACRO_DIRS interaction with
AC_REQUIRE"): Likewise.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>