AX_PREFIX_CONFIG_H and m4 quoting (was: bad m4 quotation?)

[Ralf Wildenhues]

Hello Guido,

We'd like to make you aware of an issue with the AC_CONFIG_FILES macro
that affects the AX_PREFIX_CONFIG_H macro as it is in the autoconf
archive:
http://lists.gnu.org/archive/html/bug-autoconf/2006-03/msg00038.html
(including an analysis in the following subthread; this post is actually
just following up the thread).

The gist here is that, due to backward compatibility, the first argument
of AC_CONFIG_FILES is white-space split before it is m4-expanded, and
this will cause the macro to fail loudly with the next Autoconf release.
Please consider the change mentioned in the link above which should be
backwards-compatible to Autoconf-2.50.  You could also consider
switching from ifelse to using m4_if, which has been documented since
2.52 and defined since 2.50.

We still need to document this in autoconf.texi.

Cheers,
Ralf