What steps will reproduce the problem?

runtime.TestBreakpoint does not pass on ARMv5 devices. The subprocess it spawns spins
and spins until the build times out (but the spinning child lives on quickly overloading
the machine)

http://build.golang.org/log/dd87c816b650fee49032462c4da255ff5b36d669

What is the expected output? What do you see instead?

A simpler repro is 

package main

import "runtime"

func main() {
        runtime.Breakpoint()
}

dfc@qnap:~/src$ ./bkpt 
SIGQUIT: quit
PC=0x3fca0

goroutine 1 [running]:
runtime.breakpoint()
    /home/dfc/go/src/runtime/asm_arm.s:95 fp=0x1022bfb8 sp=0x1022bfb8
runtime.Breakpoint()
    /home/dfc/go/src/runtime/proc.c:2321 +0x8 fp=0x1022bfbc sp=0x1022bfb8
main.main()
    /home/dfc/src/bkpt.go:6 +0x1c fp=0x1022bfc0 sp=0x1022bfbc
runtime.main()
    /home/dfc/go/src/runtime/proc.go:63 +0x108 fp=0x1022bfe4 sp=0x1022bfc0
runtime.goexit()
    /home/dfc/go/src/runtime/proc.c:1662 fp=0x1022bfe4 sp=0x1022bfe4

goroutine 2 [runnable]:
runtime.forcegchelper()
    /home/dfc/go/src/runtime/proc.go:90
runtime.goexit()
    /home/dfc/go/src/runtime/proc.c:1662

trap    0x6
error   0x0
oldmask 0x0
r0      0x0
r1      0x1022a200
r2      0x0
r3      0x2
r4      0xfffffade
r5      0x1c7ac
r6      0x1022bfdc
r7      0x0
r8      0x1023401c
r9      0x0
r10     0x10200140
fp      0x6adc8
ip      0x0
sp      0x1022bfb8
lr      0x370d0
pc      0x3fca0
cpsr    0x20000010
fault   0x0

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