[dev.cc] runtime/cgo: add comment about import _ "unsafe"
LGTM=bradfitz, r
R=r, bradfitz
CC=golang-codereviews
https://golang.org/cl/167650043
diff --git a/src/runtime/cgo/dragonfly.go b/src/runtime/cgo/dragonfly.go
index 96eb866..69d52b5 100644
--- a/src/runtime/cgo/dragonfly.go
+++ b/src/runtime/cgo/dragonfly.go
@@ -6,7 +6,7 @@
package cgo
-import _ "unsafe"
+import _ "unsafe" // for go:linkname
// Supply environ and __progname, because we don't
// link against the standard DragonFly crt0.o and the
