runtime: constify a test variable

Simple cleanup, no functionality change.

Change-Id: I8eceda4496a396e0117a0a601186c653982fb004
GitHub-Last-Rev: 58defc575e
GitHub-Pull-Request: golang/go#47389
Reviewed-on: https://go-review.googlesource.com/c/go/+/337289
Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Cherry Mui <cherryyz@google.com>

src/runtime/export_test.go

@@ -198,7 +198,7 @@ func MemclrBytes(b []byte) {
 	memclrNoHeapPointers(s.array, uintptr(s.len))
 }
 
-var HashLoad = &hashLoad
+const HashLoad = hashLoad
 
 // entry point for testing
 func GostringW(w []uint16) (s string) {

src/runtime/map_test.go

@@ -473,7 +473,7 @@ func TestMapNanGrowIterator(t *testing.T) {
 	nan := math.NaN()
 	const nBuckets = 16
 	// To fill nBuckets buckets takes LOAD * nBuckets keys.
-	nKeys := int(nBuckets * *runtime.HashLoad)
+	nKeys := int(nBuckets * runtime.HashLoad)
 
 	// Get map to full point with nan keys.
 	for i := 0; i < nKeys; i++ {

src/runtime/stubs.go

@@ -119,7 +119,7 @@ func reflect_memmove(to, from unsafe.Pointer, n uintptr) {
 }
 
 // exported value for testing
-var hashLoad = float32(loadFactorNum) / float32(loadFactorDen)
+const hashLoad = float32(loadFactorNum) / float32(loadFactorDen)
 
 //go:nosplit
 func fastrand() uint32 {