runtime: fix build on gri's machine
runtime: fix build on gri's machine

Why it was not failing anywhere else I don't know,
but the Makefile was definitely wrong.  The rules
must not run in parallel.

TBR=r
CC=golang-dev
http://codereview.appspot.com/5489069

dsriram/golang,apparentlymart/golang,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,dsriram/golang,apparentlymart/golang,tv42/old-go,dsriram/golang,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,gnanderson/go,tv42/old-go,dsriram/golang,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,dsriram/golang,dsriram/golang,gnanderson/go,pombredanne/go-deleteme,gnanderson/go,gnanderson/go,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,gnanderson/go,gnanderson/go,apparentlymart/golang,gnanderson/go,apparentlymart/golang,dsriram/golang,tv42/old-go,apparentlymart/golang