Arch Linux

Description:

In August, there was a change to make the go package smaller by removing "*_test.go" and testdata files from the source.

This means you can still use the toolchain and build std packages, but testing any of it is entirely broken.
For example, compare Arch's 1.17.1 versus my own source build of Go master:

```
$ wgo1 go version
go version go1.17.1 linux/amd64
$ wgo1 go test encoding/json
? encoding/json [no test files]
$ go version
go version devel go1.18-051df0d722 Wed Sep 22 03:45:00 2021 +0000 linux/amd64
$ go test encoding/json
ok encoding/json 0.533s
```

This is perhaps not critical, since most users might not notice. But I certainly have :)

The following is broken:

* Direct execution of "go test std"
* Running of "go test all" from third party modules, as nearly all import std packages
* Running third party tests that assume "std" is complete; such as https://github.com/rogpeppe/go-internal/blob/9df06c38c09b2cd3937f29c21bab94d9d165cd9d/imports/scan_test.go#L51-L53

These missing files were particularly confusing to me, because removed test files result in... no tests being run, silently.
So I do think that these files should be included in the main Go package, and not a separate "test files" package.
It's just far too easy to forget to install the latter.

As to whether or not it's OK to install std without test files: I'd say it's an incomplete install.
It happens to work for most people, but practically all software out there assumes GOROOT/src/std is complete.