bpo-39943: Add the const qualifier to pointers on non-mutable PyUnicode data. (GH-19345)

diff --git a/Modules/cjkcodecs/cjkcodecs.h b/Modules/cjkcodecs/cjkcodecs.h
index 8f6f880..e41755b 100644
--- a/Modules/cjkcodecs/cjkcodecs.h
+++ b/Modules/cjkcodecs/cjkcodecs.h
@@ -72,7 +72,7 @@
 #define ENCODER(encoding)                                               \
     static Py_ssize_t encoding##_encode(                                \
         MultibyteCodec_State *state, const void *config,                \
-        int kind, void *data,                          \
+        int kind, const void *data,                                     \
         Py_ssize_t *inpos, Py_ssize_t inlen,                            \
         unsigned char **outbuf, Py_ssize_t outleft, int flags)
 #define ENCODER_RESET(encoding)                                         \
diff --git a/Modules/cjkcodecs/multibytecodec.c b/Modules/cjkcodecs/multibytecodec.c
index a09c75d..9f9fbeb 100644
--- a/Modules/cjkcodecs/multibytecodec.c
+++ b/Modules/cjkcodecs/multibytecodec.c
@@ -228,7 +228,7 @@
         Py_ssize_t r;
         Py_ssize_t inpos;
         int kind;
-        void *data;
+        const void *data;
 
         replchar = PyUnicode_FromOrdinal('?');
         if (replchar == NULL)
@@ -457,7 +457,7 @@
     Py_ssize_t finalsize, r = 0;
     Py_ssize_t datalen;
     int kind;
-    void *data;
+    const void *data;
 
     if (PyUnicode_READY(text) < 0)
         return NULL;
diff --git a/Modules/cjkcodecs/multibytecodec.h b/Modules/cjkcodecs/multibytecodec.h
index 4d2b355..5946821 100644
--- a/Modules/cjkcodecs/multibytecodec.h
+++ b/Modules/cjkcodecs/multibytecodec.h
@@ -30,7 +30,7 @@
 typedef int (*mbcodec_init)(const void *config);
 typedef Py_ssize_t (*mbencode_func)(MultibyteCodec_State *state,
                         const void *config,
-                        int kind, void *data,
+                        int kind, const void *data,
                         Py_ssize_t *inpos, Py_ssize_t inlen,
                         unsigned char **outbuf, Py_ssize_t outleft,
                         int flags);