A build constraint reports whether the test binary was compiled with
cgo enabled, but that doesn't necessarily imply that cgo can be used
in the environment in which the test binary is run.

In particular, cross-compiled builders (such as Android) may compile
the test binaries on the host with CGO enabled but not provide a C
toolchain on the device that runs the test.

For #58775.

Change-Id: Ibf2f44c9e956cd3fa898c3de67af4449e8ef2dd1
Reviewed-on: https://go-review.googlesource.com/c/go/+/472215
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>

- Fall back to 'go env GOROOT' to locate GOROOT if runtime.GOROOT() is
  empty (as may be the case if the tool is built with -trimpath).

- Copy all of $GOROOT/android_$GOARCH/bin, not just cmd/go, to
  $GOROOT/bin.

- For consistency with CL 404134, place $GOROOT/bin at the beginning
  of $PATH, not the end.

- Don't use the install target for the "runtime" package to locate pkg/tool.
  As of Go 1.20 "runtime" doesn't have an install directory anyway.
  Since the real reason we need pkg/tool is for commands in "cmd",
  use an arbitrary command (namely "cmd/compile") to locate it.

- Use 'go list' to determine the package import path for the current
  directory, instead of assuming that it is within GOROOT or GOPATH.
  (That assumption does not hold in module mode.)

Updates #58775.

Change-Id: If76ff22bce76d05175c40678230f046a4aff0940
Reviewed-on: https://go-review.googlesource.com/c/go/+/472096
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Changkun Ou <mail@changkun.de>
Auto-Submit: Bryan Mills <bcmills@google.com>

As of CL 472096, it should work on android/arm64 always (because
internal linking is supported on that platform), and on other android
platforms when a C toolchain is present in the test environment.

Updates #58775.

Change-Id: Ifa38dc69b258b38dcc341979dcbf8cd61265c787
Reviewed-on: https://go-review.googlesource.com/c/go/+/475456
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Changkun Ou <mail@changkun.de>