Fix Py_UNICODE_TODECIMAL definition for PyPy (#6078)

* Fix Py_UNICODE_TODECIMAL definition for PyPy

* Update unicodeobject.rs

Co-authored-by: Bas Schoenmaeckers <7943856+bschoenmaeckers@users.noreply.github.com>

---------

Co-authored-by: Bas Schoenmaeckers <7943856+bschoenmaeckers@users.noreply.github.com>
Co-authored-by: David Hewitt <mail@davidhewitt.dev>

Author: 3 people

pyo3-ffi/src/cpython/unicodeobject.rs

@@ -837,6 +837,7 @@ extern_libpython! {
     // skipped _PyUnicode_ToUppercase
     // skipped _PyUnicode_ToTitlecase
 
+    #[cfg(not(PyPy))]
     fn _PyUnicode_ToDecimalDigit(ch: Py_UCS4) -> c_int;
 
     // skipped _PyUnicode_ToDigit
@@ -866,9 +867,17 @@ extern_libpython! {
 // skipped Py_UNICODE_ISNUMERIC
 // skipped Py_UNICODE_ISPRINTABLE
 
+#[cfg(not(PyPy))]
 pub unsafe extern "C" fn Py_UNICODE_TODECIMAL(ch: Py_UCS4) -> c_int {
     _PyUnicode_ToDecimalDigit(ch)
 }
+
+#[cfg(PyPy)]
+extern_libpython! {
+    #[cfg_attr(PyPy, link_name = "PyPy_UNICODE_TODECIMAL")]
+    pub fn Py_UNICODE_TODECIMAL(ch: Py_UCS4) -> c_int;
+}
+
 // skipped Py_UNICODE_TODIGIT
 // skipped Py_UNICODE_TONUMERIC