Added support for s390x

[Nayana-ibm]

Added support for linux/s390x arch in glide.
Please review.

[Nayana-ibm]

Along with this PR, we also require to add code in gox to support s390x.
Below diff will be required in https://github.com/franciscocpg/gox repo.

diff --git a/platform.go b/platform.go
index 9353b09..50820a5 100644
--- a/platform.go
+++ b/platform.go
@@ -73,6 +73,7 @@ var (
                "mips64le",
                "ppc64",
                "ppc64le",
+               "s390x",
        }

        Platforms_1_0 = []Platform{
@@ -123,7 +124,10 @@ var (
        }...)

        // Nothing changed from 1.5 to 1.6
-       Platforms_1_6 = Platforms_1_5
+       // Support for s390x
+       Platforms_1_6 = append(Platforms_1_5, []Platform{
+                {OS: "linux", Arch: "s390x", Default: true},
+       }...)
 )

 // SupportedPlatforms returns the full list of supported platforms for

To contribute for that change, we want to know about Contributor License Agreement.
I have checked URL to License: https://github.com/franciscocpg/gox/blob/master/LICENSE and
https://github.com/mitchellh/gox/blob/master/LICENSE
Please let us know which Contributor License Agreement needs for gox .

[Nayana-ibm]

@mattfarina @franciscocpg Could you please provide your inputs?

[franciscocpg]

@Nayana-ibm, i don't think that @mitchellh has any plans for merging new incoming PRs for https://github.com/mitchellh/gox. The last commit was about 1 year ago.

I think it makes sense to do something like this.

[mattfarina]

I'm going to take a look at gox vs the alternatives to see what is the best way. I'd like to cut a release soon and if there is something better now may be a good time to switch. Or, I'll look at the alternative @franciscocpg suggested.

If anyone knows of a good alternative to gox I'm interested in learning about it.

[mattfarina]

I've created Masterminds/gox (based on the great work of @franciscocpg) and added support for s390x. In #916 I moved glide to use that for cross compiling. Along with this change we should now be able to produce an s390x binary.

[Nayana-ibm]

Thanks @mattfarina It means Masterminds/gox will have s390x binaries/tar published on
https://github.com/Masterminds/glide/releases?