all: add flag for setting the goroutine stack size

This is helpful in some cases where the default stack size isn't big
enough.

transform/stacksize.go

@@ -40,7 +40,7 @@ func CreateStackSizeLoads(mod llvm.Module, config *compileopts.Config) []string
 	stackSizesGlobal := llvm.AddGlobal(mod, stackSizesGlobalType, "internal/task.stackSizes")
 	stackSizesGlobal.SetSection(".tinygo_stacksizes")
 	defaultStackSizes := make([]llvm.Value, len(functions))
-	defaultStackSize := llvm.ConstInt(functions[0].Type(), config.Target.DefaultStackSize, false)
+	defaultStackSize := llvm.ConstInt(functions[0].Type(), config.StackSize(), false)
 	for i := range defaultStackSizes {
 		defaultStackSizes[i] = defaultStackSize
 	}

transform/stacksize_test.go

@@ -13,6 +13,7 @@ func TestCreateStackSizeLoads(t *testing.T) {
 	testTransform(t, "testdata/stacksize", func(mod llvm.Module) {
 		// Run optimization pass.
 		transform.CreateStackSizeLoads(mod, &compileopts.Config{
+			Options: &compileopts.Options{},
 			Target: &compileopts.TargetSpec{
 				DefaultStackSize: 1024,
 			},