boolean, sizeofstring: update after talking with x/tools folks

sizeofstring/step3.go

@@ -1,4 +1,4 @@
-package bocchi
+package main
 
 import "unsafe"
 
@@ -16,3 +16,5 @@ var (
 	// assert y is the last field in Bocchi
 	_ [0]struct{} = [unsafe.Sizeof(Bocchi{}) - (unsafe.Alignof(Bocchi{}.y) + unsafe.Sizeof(Bocchi{}.y))]struct{}{}
 )
+
+func main() {}