compiler: add support for 'go' on func values

This commit allows starting a new goroutine directly from a func value,
not just when the static callee is known.

This is necessary to support the whole time package, not just the
commonly used subset that was compiled with the SimpleDCE pass enabled.

testdata/coroutines.go

@@ -28,6 +28,19 @@ func main() {
 	var printer Printer
 	printer = &myPrinter{}
 	printer.Print()
+
+	sleepFuncValue(func(x int) {
+		time.Sleep(1 * time.Millisecond)
+		println("slept inside func pointer", x)
+	})
+	time.Sleep(1 * time.Millisecond)
+	n := 20
+	sleepFuncValue(func(x int) {
+		time.Sleep(1 * time.Millisecond)
+		println("slept inside closure, with value:", n, x)
+	})
+
+	time.Sleep(2 * time.Millisecond)
 }
 
 func sub() {
@@ -47,6 +60,10 @@ func delayedValue() int {
 	return 42
 }
 
+func sleepFuncValue(fn func(int)) {
+	go fn(8)
+}
+
 func nowait() {
 	println("non-blocking goroutine")
 }
@@ -55,7 +72,7 @@ type Printer interface {
 	Print()
 }
 
-type myPrinter struct{
+type myPrinter struct {
 }
 
 func (i *myPrinter) Print() {

testdata/coroutines.txt

@@ -11,3 +11,5 @@ value produced after some time: 42
 non-blocking goroutine
 done with non-blocking goroutine
 async interface method call
+slept inside func pointer 8
+slept inside closure, with value: 20 8