runtime: TestNeedmDeadlock failure with SIGSEGV on linux-mips-rtrk builder

[bcmills]

2021-01-08T18:15:43-8f6a9ac/linux-mips-rtrk

--- FAIL: TestNeedmDeadlock (0.03s)
    crash_test.go:104: /tmp/gobuilder-mips64/tmp/go-build2938167109/testprogcgo.exe NeedmDeadlock exit status: exit status 2
    crash_cgo_test.go:631: want OK
        , got fatal error: unexpected signal during runtime execution
        [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x0]
        
        runtime stack:
        runtime.throw(0x57cb56, 0x2a)
        	/tmp/gobuilder-mips64/go/src/runtime/panic.go:1112 +0x60
        runtime.sigpanic()
        	/tmp/gobuilder-mips64/go/src/runtime/signal_unix.go:714 +0x3b4
        
        goroutine 17 [syscall, locked to thread]:
        runtime.goexit()
        	/tmp/gobuilder-mips64/go/src/runtime/asm_mipsx.s:635 +0x4 fp=0x83aff0 sp=0x83aff0 pc=0x47d9f8
        
        goroutine 1 [syscall]:
        main._Cfunc_runNeedmSignalThread()
        	_cgo_gotypes.go:404 +0x4c
        main.NeedmDeadlock()
        	/tmp/gobuilder-mips64/go/src/runtime/testdata/testprogcgo/needmdeadlock.go:93 +0x4c
        main.main()
        	/tmp/gobuilder-mips64/go/src/runtime/testdata/testprogcgo/main.go:34 +0x1d8
        
        goroutine 6 [runnable]:
        time.Sleep(0x1, 0x2a05f200)
        	/tmp/gobuilder-mips64/go/src/runtime/time.go:184 +0x184
        main.NeedmDeadlock.func1()
        	/tmp/gobuilder-mips64/go/src/runtime/testdata/testprogcgo/needmdeadlock.go:88 +0x48
        created by main.NeedmDeadlock
        	/tmp/gobuilder-mips64/go/src/runtime/testdata/testprogcgo/needmdeadlock.go:87 +0x44
        
FAIL
FAIL	runtime	116.006s

CC @ianlancetaylor @mengzhuo

[bcmills]

This test is new as of Go 1.16 (for #42207), so marking as release-blocker at least until we better understand the failure mode here. (CC @golang/release)

[mengzhuo]

Thanks @bcmills

I'll take a look.