Certain ios and android configurations do not yet support internal
linking.

On ios, attempting to build without cgo causes tests to fail on
essentially every run (#57961).

On android, it produces a lot of warning spam from the linker,
obscuring real problems.

Since external linking makes the result of `go install` depend on the
installed C toolchain either way, the reproducibility benefit of
disabling cgo seems minimal on these platforms anyway.

Fixes #57961.
For #24904.
Updates #57007.

Change-Id: Ied2454804e958dd670467db3d5e9ab50a40bb899
Reviewed-on: https://go-review.googlesource.com/c/go/+/463739


Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Bypass: Bryan Mills <bcmills@google.com>