Passing an argument to configure script of subproject

[ithilgore]

Hello.

I have a central projectA which relies on a library (let's say libfoo) and
another projectB which also relies on this library. libfoo resides in a
subdir in each project. The two projects are separate however.
Thus we have:
projectA/libfoo

projectB/libfoo

The problem is that in order to share libfoo between the two projects (that
is both can fetch it as an external svn object), projectA needs to pass a
certain flag to the configure script of libfoo. This flag/argument would be
something like --disable-bar where bar is something that projectA doesn't
have (It's actually another library that can be optionally linked with
libfoo but is by default linked with and needed by projectB)

The question is: How can you pass an optional argument to the configure
script of libfoo by projectA? This argument should be passed externally
only by projectA so the solution of using "configure.gnu" residing inside
libfoo wouldn't work because that way projectB would then call it too
(since libfoo should be a shared svn object between the two projects).

projectA uses a configure.ac with a AC_CONFIG_SUBDIRS directive to call the
configure script of libfoo. projectB does the same too.

By searching a bit in the configure script I saw that there is a certain
variable "ac_sub_configure_args" which if hacked in the configure script
itself and filled with a value, then that value is passed along on all
configure scripts called by AC_CONFIG_SUBDIRS. However, I found no way of
doing it normally by defining the variable in the configure.ac file. On the
other hand, this variable is then passed to all configure scripts of other
libraries that reside under projectA. So the question can be summed up to:
is there a way to pass that variable only to the configure script of libfoo
without affecting the other subprojects?

Regards.