x/build: add misc-compile-mobile TryBots for Android/iOS

[FiloSottile]

https://storage.googleapis.com/go-build-log/21200cf2/misc-compile-mobile_0b3b3144.log

/workdir/go/pkg/tool/linux_amd64/link: running gcc failed: exit status 1
/tmp/go-link-391904482/go.o:(.data+0x0): undefined reference to `x_cgo_init'
/tmp/go-link-391904482/go.o:(.data+0x4): undefined reference to `x_cgo_notify_runtime_init_done'
/tmp/go-link-391904482/go.o:(.data+0x8): undefined reference to `x_cgo_thread_start'
/tmp/go-link-391904482/go.o:(.data+0x14): undefined reference to `x_cgo_setenv'
/tmp/go-link-391904482/go.o:(.data+0x18): undefined reference to `x_cgo_unsetenv'
/tmp/go-link-391904482/go.o:(.data+0x1c): undefined reference to `_cgo_yield'
collect2: error: ld returned 1 exit status

If this is caused by my change (https://go-review.googlesource.com/c/go/+/109697) I can't see it.

/cc @bradfitz

[gopherbot]

Change https://golang.org/cl/119856 mentions this issue: dashboard: remove mobile misc-compile trybots

[bradfitz]

I guess those never worked.

We're probably missing some stuff or environment in our Dockerfile. Missing Android toolchain, etc. The Darwin one may not be possible, or we might need to do it from a Mac VM, not Docker.

/cc @eliasnaur.

[eliasnaur]

What's to do here? I think I'm missing context.

[bradfitz]

We'd like a trybot that at least compiles most things (runs make.bash) for the Android & iOS builds, even if we don't use a real device or simulator/emulator and don't actually run any tests. We have such trybots for all other ports, but not mobile.

[eliasnaur]

Ok. Is the Dockerfile from

#23824 (comment)

of any help for Android? For iOS I believe you need macOS with Xcode installed.

[bradfitz]

/cc @dmitshur

[eliasnaur]

I believe the Android part is being done as part of #23824.

[mcandre]

Seems strange for Go to claim to offer certain os, arch pairs that it can't actually build without an external toolchain setup

[ianlancetaylor]

@mcandre What do you suggest we do? It doesn't seem to make sense to say that we don't support these systems.