cmd/link: handle dynamic import variables on Darwin in plugin mode

CL 501855 added support for cgo_dynamic_import variables on Darwin.
But it didn't support the plugin build mode on amd64, where the
assembler turns a direct load (R_PCREL) to a load via GOT
(R_GOTPCREL). This CL adds the support. We just need to handle
external linking mode, as this can only occur in plugin or shared
build mode, which requires external linking.

Fixes #67976.
Updates #50891.

Change-Id: I0f56265d50bfcb36047fa5538ad7a5ec77e7ef96
Reviewed-on: https://go-review.googlesource.com/c/go/+/592499
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/src/cmd/cgo/internal/testplugin/testdata/issue67976/plugin.go b/src/cmd/cgo/internal/testplugin/testdata/issue67976/plugin.go
new file mode 100644
index 0000000000..502ecc5c47
--- /dev/null
+++ b/src/cmd/cgo/internal/testplugin/testdata/issue67976/plugin.go
@@ -0,0 +1,16 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"io"
+	"runtime/pprof"
+)
+
+func main() {}
+
+func Start() {
+	pprof.StartCPUProfile(io.Discard)
+}