cmd/go: tests are skipped when GOOS/GOARCH do not match the installed toolchain

[bcmills]

The test binary for cmd/go currently skips itself completely when its GOOS or GOARCH doesn't match the GOOS or GOARCH of the installed toolchain:
https://cs.opensource.google/go/go/+/master:src/cmd/go/go_test.go;l=196-214;drc=c2edb2c841149f2e56963071065d52247e24092a

Unfortunately, that makes it much more difficult than necessary to diagnose test failures that are specific to a GOOS or GOARCH, especially when those tests can be run natively (such as for 386 on an amd64 host) or under emulation (such as for tests that happen to mostly-work under QEMU).

The problem is especially acute now that we have fuzzing: 386 builds lack fuzzer instrumentation (so tests on that architecture behave substantially differently than on amd64), and many tests of the fuzzer are implemented as cmd/go script tests so that they can check the behavior of go test -fuzz=. end-to-end.

I have a pending fix for this in CL 356611.

[gopherbot]

Change https://go.dev/cl/356611 mentions this issue: cmd/go: run tests when cmd/go is cross-compiled