arm: automatically determine stack sizes

This is a big change that will determine the stack size for many
goroutines automatically. Functions that aren't recursive and don't call
function pointers can in many cases have an automatically determined
worst case stack size. This is useful, as the stack size is usually much
lower than the previous hardcoded default of 1024 bytes: somewhere
around 200-500 bytes is common.

A side effect of this change is that the default stack sizes (including
the stack size for other architectures such as AVR) can now be changed
in the config JSON file, making it tunable per application.

src/internal/task/task_stack.go

@@ -54,7 +54,7 @@ func (t *Task) Resume() {
 }
 
 // initialize the state and prepare to call the specified function with the specified argument bundle.
-func (s *state) initialize(fn uintptr, args unsafe.Pointer) {
+func (s *state) initialize(fn uintptr, args unsafe.Pointer, stackSize uintptr) {
 	// Create a stack.
 	stack := make([]uintptr, stackSize/unsafe.Sizeof(uintptr(0)))
 
@@ -67,9 +67,9 @@ func runqueuePushBack(*Task)
 
 // start creates and starts a new goroutine with the given function and arguments.
 // The new goroutine is scheduled to run later.
-func start(fn uintptr, args unsafe.Pointer) {
+func start(fn uintptr, args unsafe.Pointer, stackSize uintptr) {
 	t := &Task{}
-	t.state.initialize(fn, args)
+	t.state.initialize(fn, args, stackSize)
 	runqueuePushBack(t)
 }