runtime: support register ABI for finalizers

This change modifies runfinq to properly pass arguments to finalizers in
registers via reflectcall.

For #40724.

Change-Id: I414c0eff466ef315a0eb10507994e598dd29ccb2
Reviewed-on: https://go-review.googlesource.com/c/go/+/300112
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/runtime/export_test.go

@@ -1220,3 +1220,18 @@ func (th *TimeHistogram) Count(bucket, subBucket uint) (uint64, bool) {
 func (th *TimeHistogram) Record(duration int64) {
 	(*timeHistogram)(th).record(duration)
 }
+
+func SetIntArgRegs(a int) int {
+	lock(&finlock)
+	old := intArgRegs
+	intArgRegs = a
+	unlock(&finlock)
+	return old
+}
+
+func FinalizerGAsleep() bool {
+	lock(&finlock)
+	result := fingwait
+	unlock(&finlock)
+	return result
+}