[dev.regabi] cmd/compile: process //go:linknames after declarations
Allows emitting errors about ineffectual //go:linkname directives.
In particular, this exposed: a typo in os2_aix.go; redundant (but
harmless) directives for libc_pipe in both os3_solaris.go and
syscall2_solaris.go; and a bunch of useless //go:linkname directives
in macOS wrapper code.
However, because there's also ineffectual directives in the vendored
macOS code from x/sys, that can't be an error just yet. So instead we
print a warning (including a heads up that it will be promoted to an
error in Go 1.17) to prevent backsliding while we fix and re-vendor
that code.
Passes toolstash-check.
Change-Id: I59badeab5df0d8b3abfd14c6066e9bb00e840f73
Reviewed-on: https://go-review.googlesource.com/c/go/+/273986
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Russ Cox <rsc@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>