runtime: comment that some linknames are used by runtime/trace

Change-Id: I118d1ee09dfd6fd0075f9e5eeeb54441328bff4d
Reviewed-on: https://go-review.googlesource.com/c/go/+/681495
Reviewed-by: Michael Knyszek <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Carlos Amedee <[email protected]>

Author: cherrymui

src/runtime/trace.go

@@ -331,7 +331,7 @@ func StopTrace() {
 //
 // traceAdvanceSema must not be held.
 //
-// traceAdvance is called by golang.org/x/exp/trace using linkname.
+// traceAdvance is called by runtime/trace and golang.org/x/exp/trace using linkname.
 //
 //go:linkname traceAdvance
 func traceAdvance(stopTrace bool) {

src/runtime/tracetime.go

@@ -51,7 +51,7 @@ type traceTime uint64
 // nosplit because it's called from exitsyscall and various trace writing functions,
 // which are nosplit.
 //
-// traceClockNow is called by golang.org/x/exp/trace using linkname.
+// traceClockNow is called by runtime/trace and golang.org/x/exp/trace using linkname.
 //
 //go:linkname traceClockNow
 //go:nosplit