x/tools/go/loader: TestCgoOption fails on GOOS=darwin

[findleyr]

@pjweinb pointed out that TestCgoOption fails on GOOS=darwin.

I'm on linux, but after hacking up that test, I can reproduce:

go test ./go/loader -run=TestCgoOption
--- FAIL: TestCgoOption (1.42s)
    stdlib_test.go:178: /home/rfindley/src/go/src/net/cgo_unix.go:62:6: func net.cgoLookupHost(ctx context.Context, name string) (hosts []string, err error, completed bool) (CgoEnabled=false)
    stdlib_test.go:187: CGO_ENABLED=0: func net.cgoLookupHost(ctx context.Context, name string) (hosts []string, err error, completed bool) found in cgo_unix.go, want cgo_stub.go
    stdlib_test.go:178: /home/rfindley/src/go/src/net/cgo_unix.go:62:6: func net.cgoLookupHost(ctx context.Context, name string) (hosts []string, err error, completed bool) (CgoEnabled=true)
    stdlib_test.go:178: /home/rfindley/src/go/src/os/user/cgo_lookup_unix.go:18:6: func os/user.current() (*os/user.User, error) (CgoEnabled=false)
    stdlib_test.go:187: CGO_ENABLED=0: func os/user.current() (*os/user.User, error) found in cgo_lookup_unix.go, want lookup_stubs.go
    stdlib_test.go:178: /home/rfindley/src/go/src/os/user/cgo_lookup_unix.go:18:6: func os/user.current() (*os/user.User, error) (CgoEnabled=true)
FAIL
FAIL    golang.org/x/tools/go/loader    1.446s
FAIL

Based on that failure, it looks like the test depends on the location of certain functions across a build-tagged package, to verify that package loading is correctly honoring GOOS/GOARCH. That is bound to eventually run into this type of failure; we should rewrite the test to load a fixed set of testdata packages.

More generally, I think this test may have been failing for a long time, and we never noticed because we don't have darwin longtest builders.

[gopherbot]

Change https://go.dev/cl/467695 mentions this issue: go/loader: temporarily skip TestCgoOption on darwin