wasm: don't block //go:wasmexport because of running goroutines

This fixes bug https://github.com/tinygo-org/tinygo/issues/4874.

testdata/wasmexport-noscheduler.go

@@ -39,3 +39,9 @@ func reentrantCall(a, b int32) int32 {
 	println("reentrantCall result:", result)
 	return result
 }
+
+//go:wasmexport goroutineExit
+func goroutineExit() {
+	// Dummy, not a real test (since we have no scheduler).
+	println("goroutineExit: exit")
+}

testdata/wasmexport.go

@@ -1,6 +1,9 @@
 package main
 
-import "time"
+import (
+	"runtime"
+	"time"
+)
 
 func init() {
 	println("called init")
@@ -50,3 +53,15 @@ func reentrantCall(a, b int32) int32 {
 	println("reentrantCall result:", result)
 	return result
 }
+
+// Test for bug: https://github.com/tinygo-org/tinygo/issues/4874
+//
+//go:wasmexport goroutineExit
+func goroutineExit() {
+	go func() {
+		time.Sleep(time.Second * 10)
+		println("goroutineExit: exiting goroutine")
+	}()
+	runtime.Gosched()
+	println("goroutineExit: exit")
+}

testdata/wasmexport.js

@@ -15,6 +15,7 @@ function runTests() {
     testCall('add', [6, 1], 7);
     testCall('reentrantCall', [2, 3], 5);
     testCall('reentrantCall', [1, 8], 9);
+    testCall('goroutineExit', [], undefined);
 }
 
 let go = new Go();

testdata/wasmexport.txt

@@ -9,3 +9,4 @@ reentrantCall result: 5
 reentrantCall: 1 8
 called add: 1 8
 reentrantCall result: 9
+goroutineExit: exit