Define missing import APIs

I need some of these APIs for the pyembed crate (used as part of
PyOxidizer). I figured I might as well define them all.

All these APIs are limited.

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Add #[pyo3(from_py_with = "...")]` attribute for function arguments and struct fields to override the default from-Python conversion. [#1411](https://github.com/PyO3/pyo3/pull/1411)
 - Add FFI definition `PyCFunction_CheckExact` for Python 3.9 and later. [#1425](https://github.com/PyO3/pyo3/pull/1425)
 - Add FFI definition `Py_IS_TYPE`. [#1429](https://github.com/PyO3/pyo3/pull/1429)
+- Add FFI definitions for limited APIs `PyImport_ExtendInittab` and missing `_PyImport_*` functions.
 
 ### Changed
 - Change `PyTimeAcces::get_fold()` to return a `bool` instead of a `u8`. [#1397](https://github.com/PyO3/pyo3/pull/1397)

src/ffi/import.rs

@@ -1,4 +1,6 @@
 use crate::ffi::object::PyObject;
+#[cfg(not(Py_LIMITED_API))]
+use std::os::raw::c_uchar;
 use std::os::raw::{c_char, c_int, c_long};
 
 extern "C" {
@@ -82,3 +84,68 @@ extern "C" {
         initfunc: Option<extern "C" fn() -> *mut PyObject>,
     ) -> c_int;
 }
+
+#[repr(C)]
+#[derive(Copy, Clone)]
+#[cfg(not(Py_LIMITED_API))]
+pub struct _inittab {
+    pub name: *mut c_char,
+    pub initfunc: Option<unsafe extern "C" fn()>,
+}
+
+#[repr(C)]
+#[derive(Copy, Clone)]
+#[cfg(not(Py_LIMITED_API))]
+pub struct _frozen {
+    pub name: *const c_char,
+    pub code: *const c_uchar,
+    pub size: c_int,
+}
+
+#[cfg(not(Py_LIMITED_API))]
+extern "C" {
+    pub static mut PyImport_FrozenModules: *const _frozen;
+    pub static mut PyImport_Inittab: *mut _inittab;
+
+    pub fn PyImport_ExtendInittab(newtab: *const _inittab) -> c_int;
+
+    #[cfg(not(Py_3_7))]
+    pub fn _PyImport_FindBuiltin(name: *const c_char) -> *mut PyObject;
+    #[cfg(all(Py_3_7, not(Py_3_9)))]
+    pub fn _PyImport_FindBuiltin(name: *const c_char, modules: *mut PyObject) -> *mut PyObject;
+
+    pub fn _PyImport_FindExtensionObject(
+        name: *mut PyObject,
+        filename: *mut PyObject,
+    ) -> *mut PyObject;
+
+    #[cfg(all(Py_3_7, not(Py_3_9)))]
+    pub fn _PyImport_FindExtensionObjectEx(
+        name: *mut PyObject,
+        filename: *mut PyObject,
+        modules: *mut PyObject,
+    ) -> *mut PyObject;
+
+    #[cfg(not(Py_3_7))]
+    pub fn _PyImport_FixupBuiltin(module: *mut PyObject, name: *const c_char) -> c_int;
+    #[cfg(Py_3_7)]
+    pub fn _PyImport_FixupBuiltin(
+        module: *mut PyObject,
+        name: *const c_char,
+        modules: *mut PyObject,
+    ) -> c_int;
+
+    #[cfg(not(Py_3_7))]
+    pub fn _PyImport_FixupExtensionObject(
+        module: *mut PyObject,
+        name: *mut PyObject,
+        filename: *mut PyObject,
+    ) -> c_int;
+    #[cfg(Py_3_7)]
+    pub fn _PyImport_FixupExtensionObject(
+        module: *mut PyObject,
+        name: *mut PyObject,
+        filename: *mut PyObject,
+        modules: *mut PyObject,
+    ) -> c_int;
+}