configure.ac parameter

[Alex Farber]

Currently I have the following code to build wxWidgets program with
autotools:

configure.ac:

WX_CPP="`wx-config --cppflags`"
AC_SUBST(WX_CPP)
WX_LIBS="`wx-config --libs`"
AC_SUBST(WX_LIBS)

Makefile.am:

AM_CXXFLAGS = $(WX_CPP)
program_LDADD = $(WX_LIBS)

This works fine. Now I want to use WX_CPP and WX_LIBS as configure script
parameters, allowing to change default values. I need to run the configure
script by the following way:

./configure WX_CPP="`cpp-flags-program`" WX_LIBS="`lib-flags-program`"

or:

./configure WX_CPP="compiler flags..." WX_LIBS="linker flags..."

This doesn't work, because AC_SUBST is done when configure script is
generated, and not when it is executed. Is there some way to get it working?