runtime: avoid malloc during malloc
runtime: avoid malloc during malloc

A fault during malloc might lead to the program's
first call to findfunc, which would in turn call malloc.
Don't do that.

Fixes issue 1777.

R=golang-dev, gri
CC=golang-dev
http://codereview.appspot.com/5689047

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