Don't build proctrack/aix if a proper proctrackext.emp is not specified

but don't stop the rest of the build

auxdir/x_ac_aix.m4

@@ -43,8 +43,14 @@ AC_DEFUN([X_AC_AIX],
          [ PROCTRACKDIR="$withval" ]
       )
       if test ! -d "$PROCTRACKDIR" -o ! -f "$PROCTRACKDIR/proctrackext.exp"; then
-         AC_MSG_ERROR([$PROCTRACKDIR/proctrackext.exp is required and does not exist])
+         AC_MSG_WARN([proctrackext.exp is required for AIX proctrack support, specify location with --with-proctrack])
+         ac_have_aix_proctrack="no"
+      else
+         AC_SUBST(PROCTRACKDIR)
+         ac_have_aix_proctrack="yes"
       fi
-      AC_SUBST(PROCTRACKDIR)
+   else
+      ac_have_aix_proctrack="no"
    fi
+   AM_CONDITIONAL(HAVE_AIX_PROCTRACK, test "x$ac_have_aix_proctrack" = "xyes")
 ])

src/plugins/proctrack/Makefile.am

 # $Id$
 # Makefile for proctrack plugins
 
-if HAVE_AIX
+if HAVE_AIX_PROCTRACK
 SUBDIRS = aix sid
 else
 SUBDIRS = sid