dist: add binary download for cross compilation

[adg]

A recent post to the mailing list:
https://groups.google.com/d/msg/golang-nuts/oFIs6Puj0_Q/0_seVYRtOyYJ
suggests we include binary downloads of a cross-compiled toolchain.

It's relatively easy to do, and would benefit people who run build farms. Probably we
should only offer it for the most popular platforms (darwin/linux/windows amd64 only).

[minux]

Comment 1:

we probably should consider the impact of not support cgo.
(a particular annoying problem is os/user.Current doesn't work without cgo
on unix)
also, i suggest we add distributions for arm cross toolchains too.
i have an idea:
1. we make misc/dist build all part of toolchain for all distribution tarballs (e.g.
windows/amd64 tarball should
contain 5g, 5c, 8g, 8c, etc)
2. we release an additional cross compilation tarball that contains compiled pkgs for
all supported platforms.
so that people can download that and properly extract into there $GOROOT/pkg and
immediately get
cross compilation capabilities without ever compiling the Go source code.
as a refinement to 2, we can divide that into cross compliation "addon" for different
OSes, e.g.
windows.zip contains pkg/windows_amd64 and pkg/windows_386
linux.zip contains pkg/linux_amd64, pkg/linux_386, and pkg/linux_arm, etc.
in this way we don't need to provide O(N^2) (N is supported platforms) tarballs to
support every case,
and yet we add full (non-cgo) cross compilation support for binary distribution users.

[rsc]

Comment 2:

Labels changed: added go1.3maybe.

[rsc]

Comment 4:

Labels changed: added release-none, removed go1.3maybe.

[rsc]

Comment 5:

Labels changed: added repo-main.

[mattn]

Comment 6:

pw_dir in struct passwd on OSX is at different offset of linux's one.
So if we use cross compilation, HomeDir should be broken that derefered from broken
offset pointer.

[mattn]

Comment 7:

We write often codes that get configuration via ~/.config/xxx. And We use cross
compilation for that. But we can't provide OSX binaries because os/user.Current()
doesn't work with cross compilation.

[minux]

Comment 8:

Re #7, for os/user and net on platforms with binary distribution,
there is a way to cross compile packages using those packages
without setting up a gcc/clang cross-compiler.
for example, see gonative:
https://inconshreveable.com/04-30-2014/cross-compiling-golang-programs-with-native-libraries/

[dominikh]

Is this still relevant, now that Go cross compilation works without having to do anything special?

[bradfitz]

Probably not relevant. Most of this bug has been discussing os/user not working without cgo, but that was fixed in #14626 too.

Closing.