runtime: allow for 5 more threads in TestWindowsStackMemory*

Original version of TestWindowsStackMemory did not consider sysmon and
other threads running during the test. Allow for 5 extra threads in this
test - this should cover any new threads in the future.

Fixes #58570

Change-Id: I215790f9b94ff40a32ddd7aa54af715d1dc391c6
Reviewed-on: https://go-review.googlesource.com/c/go/+/473415
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

src/runtime/testdata/testprog/syscall_windows.go

@@ -66,5 +66,8 @@ func StackMemory() {
 	if err != nil {
 		panic(err)
 	}
-	print((mem2 - mem1) / threadCount)
+	// assumes that this process creates 1 thread for each
+	// thread locked goroutine plus extra 5 threads
+	// like sysmon and others
+	print((mem2 - mem1) / (threadCount + 5))
 }

src/runtime/testdata/testprogcgo/stack_windows.go

@@ -50,5 +50,8 @@ func StackMemory() {
 	if err != nil {
 		panic(err)
 	}
-	print((mem2 - mem1) / threadCount)
+	// assumes that this process creates 1 thread for each
+	// thread locked goroutine plus extra 5 threads
+	// like sysmon and others
+	print((mem2 - mem1) / (threadCount + 5))
 }