cmd/link: linker should fail quickly when external link mode is not supported

[jeremyfaller]

What version of Go are you using (go version)?

HEAD

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

go env Output

darwin, 386

What did you do?

While investigating Issue 33808 I discovered that external linking doesn't work in 32bit darwin.

What did you expect to see?

Linker should fail quickly when trying to do an external link.

What did you see instead?

Linker calls external linker, external linker fails.

CC @cherrymui

[laboger]

External linking is supported on ppc64le, but not on ppc64. If we try to link externally we see this:

go build -ldflags '-linkmode=external' hello.go
# command-line-arguments
/home/boger/golang/base/go/pkg/tool/linux_ppc64/link: external linking not supported for linux/ppc64

[jeremyfaller]

Thanks, @laboger. The problem was discovered with darwin/32-bit (which for recent versions of darwin don't support external linking), and was filed as a generic bug. Thanks for checking PPC.