examples: conditionally compile an `asm amd64 {}` block on M1 in asm.v

examples/asm.v

@@ -2,13 +2,15 @@ fn main() {
 	a := 100
 	b := 20
 	mut c := 0
-	asm amd64 {
-		mov eax, a
-		add eax, b
-		mov c, eax
-		; =r (c) // output
-		; r (a) // input
-		  r (b)
+	$if amd64 {
+		asm amd64 {
+			mov eax, a
+			add eax, b
+			mov c, eax
+			; =r (c) // output
+			; r (a) // input
+			  r (b)
+		}
 	}
 	println('a: $a') // 100
 	println('b: $b') // 20