runtime: add reference to debugPinnerV1

This is intended to be used by debuggers, to keep heap memory reachable
even if it isn't referenced from anywhere else.

Change-Id: I1e900e02b4fe3a188f8173cec70f8de32122489b
Reviewed-on: https://go-review.googlesource.com/c/go/+/682875
Reviewed-by: abner chenc <chenguoqi@loongson.cn>
Reviewed-by: Mark Freeman <mark@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: limeidan

src/runtime/asm_loong64.s

@@ -70,8 +70,9 @@ nocgo:
 	// start this M
 	JAL	runtime·mstart(SB)
 
-	// Prevent dead-code elimination of debugCallV2, which is
+	// Prevent dead-code elimination of debugCallV2 and debugPinnerV1, which are
 	// intended to be called by debuggers.
+	MOVV	$runtime·debugPinnerV1<ABIInternal>(SB), R0
 	MOVV	$runtime·debugCallV2<ABIInternal>(SB), R0
 
 	MOVV	R0, 1(R0)