travis: Enable 32-bit little endian MIPS on linux-next

[nathanchance]

All of the necessary patches have been applied to their respective trees and they are all available in linux-next.

This requires a bump in the Docker image first: https://github.com/ClangBuiltLinux/dockerimage/pull/35

Presubmit will be run once that change has been merged.

[nathanchance]

I’ll wait for presubmit to come back before merging but it should be!

[nickdesaulniers]

Let's add a patch file instead? (for -Wno-implicit-fallthrough)

[nathanchance]

I can do that if you want me to but that file needs to be applied for every architecture meaning that when that patch gets applied, that entire repo will go red. I'm currently testing:

https://github.com/nathanchance/continuous-integration/commits/fix-everything

https://travis-ci.com/nathanchance/continuous-integration/builds/124807169

[nickdesaulniers]

LGTM?

[nathanchance]

I'll rebase this on #205 if that is okay?

[nathanchance]

Presubmit: https://travis-ci.com/nathanchance/continuous-integration/builds/125000854