xbps-src: only use /cachedir in chroot, if it was set in conffile.

xbps-src/shutils/chroot.sh.in

@@ -77,7 +77,6 @@ XBPS_MASTERDIR=/
 XBPS_CFLAGS="$XBPS_CFLAGS"
 XBPS_CXXFLAGS="$XBPS_CFLAGS"
 XBPS_LDFLAGS="$XBPS_LDFLAGS"
-XBPS_CACHEDIR=/cachedir
 XBPS_FETCH_CMD="xbps-uhelper.static fetch"
 XBPS_COMPRESS_CMD="$XBPS_COMPRESS_CMD"
 _EOF
@@ -91,6 +90,9 @@ fi
 if [ -n "$XBPS_COMPRESS_LEVEL" ]; then
 	echo "XBPS_COMPRESS_LEVEL=$XBPS_COMPRESS_LEVEL" >> $XBPSSRC_CF
 fi
+if [ -n "$XBPS_CACHEDIR" ]; then
+	echo "XBPS_CACHEDIR=/cachedir" >> $XBPSSRC_CF
+fi
 
 echo "# End of configuration file." >> $XBPSSRC_CF