wasm: support -scheduler=none

Previously, -scheduler=none wasn't possible for WASM targets:

    $ tinygo run -target=wasm -scheduler=none ./testdata/stdlib.go
    src/runtime/runtime_wasm_js.go:34:2: attempted to start a goroutine without a scheduler

With this commit, it works just fine:

    $ tinygo run -target=wasm -scheduler=none ./testdata/stdlib.go
    stdin:  /dev/stdin
    stdout: /dev/stdout
    stderr: /dev/stderr
    pseudorandom number: 1298498081
    strings.IndexByte: 2
    strings.Replace: An-example-string

Supporting `-scheduler=none` has some benefits:

  * it reduces file size a lot compared to having a scheduler
  * it allows JavaScript to call exported functions

main_test.go

@@ -164,7 +164,7 @@ func runPlatTests(options compileopts.Options, tests []string, t *testing.T) {
 		t.Parallel()
 		runTest("env.go", options, t, []string{"first", "second"}, []string{"ENV1=VALUE1", "ENV2=VALUE2"})
 	})
-	if options.Target == "wasi" {
+	if options.Target == "wasi" || options.Target == "wasm" {
 		t.Run("alias.go-scheduler-none", func(t *testing.T) {
 			t.Parallel()
 			options := compileopts.Options(options)

src/runtime/runtime_wasm_js.go

@@ -29,34 +29,6 @@ func setEventHandler(fn func()) {
 	handleEvent = fn
 }
 
-//export resume
-func resume() {
-	go func() {
-		handleEvent()
-	}()
-
-	if wasmNested {
-		minSched()
-		return
-	}
-
-	wasmNested = true
-	scheduler()
-	wasmNested = false
-}
-
-//export go_scheduler
-func go_scheduler() {
-	if wasmNested {
-		minSched()
-		return
-	}
-
-	wasmNested = true
-	scheduler()
-	wasmNested = false
-}
-
 func ticksToNanoseconds(ticks timeUnit) int64 {
 	// The JavaScript API works in float64 milliseconds, so convert to
 	// nanoseconds first before converting to a timeUnit (which is a float64),

src/runtime/runtime_wasm_js_scheduler.go

@@ -0,0 +1,32 @@
+//go:build wasm && !wasi && !scheduler.none
+// +build wasm,!wasi,!scheduler.none
+
+package runtime
+
+//export resume
+func resume() {
+	go func() {
+		handleEvent()
+	}()
+
+	if wasmNested {
+		minSched()
+		return
+	}
+
+	wasmNested = true
+	scheduler()
+	wasmNested = false
+}
+
+//export go_scheduler
+func go_scheduler() {
+	if wasmNested {
+		minSched()
+		return
+	}
+
+	wasmNested = true
+	scheduler()
+	wasmNested = false
+}