mozilla's configure.in

[Chris Seawood]

Hi, I'm the build maintainer for Mozilla.  One of our developers filed a 
bug stating that autoconf 2.52 doesn't like our configure.in, 
http://bugzilla.mozilla.org/show_bug.cgi?id=104642 .

This is partially understandable as we do some bad things like calling 
AC_OUTPUT_SUBDIRS manually so that we can add options to subconfigures. 
 However, the problem that he was getting hung up on was that autoconf 
only expands some macros once, while our configure.in calls some of them 
twice.  Specifically, we do:

if test -n "$CROSS_COMPILE"; then
<check for HOST_CC>
<check for CC searching ${target}-gcc && ${target_alias}-gcc>
AC_PROG_CC - to actually run the compile test
else
AC_PROG_CC
<set HOST_CC=CC>
fi

He was told that this was wrong.  Specifically,he was told:

> That's correct, using conditional checking with Autoconf is a very bad
> idea.  You should never do that.  Always check, and perform
> conditional actions, but don't make conditional checks.

I probably zoned out on the discussion that covered this but what was 
the purpose of only expanding the macros once?

(And yes, I know s/HOST/BUILD/ , s/host/build/ etc etc.)

- cls