[Docker-maint] Bug#784543: [pkg-golang-devel] Bug#784543: golang: test failures on arm64

[Edmund Grimley Evans]

I think I've resolved a couple of the issues:

* Not building with gccgo:

I thought I was joking when I wrote that I sometimes forget to mount
/proc. Well, it turns out that the build system runs "go env GOROOT",
and that command fails obscurely if /proc is not mounted:

$ go env GOROOT
fatal error: libbacktrace could not find executable to open

runtime stack:
panic during panic

runtime stack:
stack trace unavailable

Maybe someone should make that failure more user-friendly. I have seen
programs that tell you exactly how to mount /proc.

Anyway, I was then able to build golang from gccgo-5.

* The GDB failure:

This seems to pass with the newer gdb installed, or with no gdb
installed; gdb is not installed by the Build-Depends.

I still have the other two failures, but I think these don't affect
the buildds or typical set-ups:

--- FAIL: TestIPv4MulticastListener (0.00s)
    listen_test.go:556: 224.0.0.254 not found in multicast rib
FAIL
FAIL    net    1.871s

--- FAIL: TestCloneNEWUSERAndRemapNoRootDisableSetgroups (0.00s)
    exec_linux_test.go:53: Cmd failed with err fork/exec
/usr/bin/whoami: operation not permitted, output:
FAIL
FAIL    syscall    0.069s