[pkg-go] Please give back golang-golang-x-tools (1:0.0~git20170707.0.bce9606b+ds-1) on s390x

[Anthony Fok]

Hello,

Seeing the latest build log at:

    https://buildd.debian.org/status/logs.php?pkg=golang-golang-x-tools&arch=s390x

It seems that golang-golang-x-tools is experiencing "SIGILL: illegal
instruction" during the "go test" run on s390x on zemlinsky, even it
is using the supposedly z10-compatible gccgo-7.

The same tests ran perfectly when I tested the package on zelenka
s390x porterbox.

    gb golang-golang-x-tools_1:0.0~git20170707.0.bce9606b+ds-1 . s390x

Many thanks!

Side discussion: I don't know if it is an isolated incident or not,
and whether it is easy to patch/workaround, but if gccgo-7 and beyond
are not backward compatible with z10 CPU instructions, perhaps we
should eventually switch back to using the golang-go as default for
s390x?

Cheers,
Anthony