Use values exported from $(TOPDIR)/rules.mk for determining
	the target system instead of the host configuration

Index: ppp-2.4.3/configure
===================================================================
--- ppp-2.4.3.orig/configure	2007-06-04 13:22:08.549555552 +0200
+++ ppp-2.4.3/configure	2007-06-04 13:22:08.618545064 +0200
@@ -8,9 +8,9 @@
 #  if [ -d /NextApps ]; then
 #    system="NeXTStep"
 #  else
-  system=`uname -s`
-  release=`uname -r`
-  arch=`uname -m`
+  system=${UNAME_S:-`uname -s`}
+  release=${UNAME_R:-`uname -r`}
+  arch=${UNAME_M:-`uname -m`}
 #  fi
 state="unknown"