AC_CHECK_LIB not substituting LDFLAGS

[Jose Roman Bilbao <jrbcast at teleline dot es>]

Hi,

I am trying to test if VTK library is installed on my system. As it is
not installed on a regular PATH I would like something that test for a
--with-vtk-libdir existence. If it does exist it should be added to
LDFLAGS and then test using AC_CHECK_LIB but I can not get it to work:

AC_ARG_WITH(vtk-libdir,[  --with-vtk-libdir=DIR           location of
the gd lib/inc],  [LDFLAGS="${LDFLAGS} -L${withval} -lvtkCommon
-lvtkImaging"])


# If vtk is not found and no valid --with-vtk-libdir PATH
# has been provide configuration finishes
AC_MSG_RESULT($LDFLAGS)


AC_MSG_RESULT will return empty string... How can I make AC_ARG_WITH
modifies LDFLAGS variable?.

Thanks,

-- 
Jose Roman Bilbao <jrbcast@teleline.es>