Initialize ast when calling compile function (RustPython#4462)

Author: garychia

vm/src/vm/mod.rs

@@ -247,6 +247,8 @@ impl VirtualMachine {
         let mut essential_init = || -> PyResult {
             #[cfg(not(target_arch = "wasm32"))]
             import::import_builtin(self, "_signal")?;
+            #[cfg(any(feature = "parser", feature = "compiler"))]
+            import::import_builtin(self, "_ast")?;
             #[cfg(not(feature = "threading"))]
             import::import_frozen(self, "_thread")?;
             let importlib = import::init_importlib_base(self)?;