Fix compiler warnings

Modules/_io/textio.c

@@ -1431,7 +1431,7 @@ textiowrapper_read_chunk(textio *self, Py_ssize_t size_hint)
 
     /* Read a chunk, decode it, and put the result in self._decoded_chars. */
     if (size_hint > 0) {
-        size_hint = Py_MAX(self->b2cratio, 1.0) * size_hint;
+        size_hint = (Py_ssize_t)(Py_MAX(self->b2cratio, 1.0) * size_hint);
     }
     chunk_size = PyLong_FromSsize_t(Py_MAX(self->chunk_size, size_hint));
     if (chunk_size == NULL)

Modules/posixmodule.c

@@ -7756,9 +7756,9 @@ posix_putenv(PyObject *self, PyObject *args)
     PyObject *os1, *os2;
     char *s1, *s2;
     char *newenv;
+    size_t len;
 #endif
     PyObject *newstr = NULL;
-    size_t len;
 
 #ifdef MS_WINDOWS
     if (!PyArg_ParseTuple(args,

Objects/unicodeobject.c

@@ -4330,7 +4330,8 @@ static int
 refit_partial_string(PyObject **unicode, int kind, void *data, Py_ssize_t n)
 {
     PyObject *tmp;
-    Py_ssize_t k, maxchar;
+    Py_ssize_t k;
+    Py_UCS4 maxchar;
     for (k = 0, maxchar = 0; k < n; k++)
         maxchar = Py_MAX(maxchar, PyUnicode_READ(kind, data, k));
     tmp = PyUnicode_New(PyUnicode_GET_LENGTH(*unicode), maxchar);