Forbid AX_-prefixed patterns more selectively

We want to make autoconf fail early and with a user-comprehensible
message if autoconf-archive isn't installed, rather than generating
a configure script with syntax errors, or a configure script that runs
successfully but doesn't do what we intended.

However, autoconf-archive doesn't actually guarantee not to use
AX_-prefixed shell variable names without m4_pattern_allow'ing them
(unlike Autoconf, Automake, Libtool and pkg-config, which explicitly use
m4_pattern_allow for variables with AC_, AM_, LT_ and PKG_ prefixes), so
it isn't safe to assume that they won't be used. In particular, recent
versions of AX_CHECK_GNU_MAKE appear to be using
$AX_CHECK_GNU_MAKE_HEADLINE as a shell variable.

Instead, specifically forbid the names of the finite list of macros
that we actually use.

Signed-off-by: Simon McVittie <>
Resolves: dbus#249
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