change the definition of uconv to enable boostrapping without
preexisting binaries.

Reference: /n/atom/patch/applied2013/rtbootstrap
Date: Fri Oct 25 02:21:00 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/runetype/mkfile	Fri Oct 25 02:20:39 2013
+++ /sys/src/cmd/runetype/mkfile	Fri Oct 25 02:20:39 2013
@@ -4,7 +4,7 @@
 <|mkrunesize
 url=http://www.unicode.org/Public/UNIDATA/
 <|sed -n ''''s/^([A-Z])/cpu\1/p''''  </$cputype/mkfile
-uconv=/$cputype/bin/rune/uconv
+uconv=$cpuO.uconv
 CLIB=/sys/src/libc/port
 ULIB=/lib
 BIN=/$objtype/bin/rune