bpo-33012: Fix invalid function cast warnings with gcc 8 in Argument Clinic. (GH-6748)

Fix invalid function cast warnings with gcc 8
for method conventions different from METH_NOARGS, METH_O and
METH_VARARGS in Argument Clinic generated code.
diff --git a/Objects/clinic/bytesobject.c.h b/Objects/clinic/bytesobject.c.h
index c781948..193d534 100644
--- a/Objects/clinic/bytesobject.c.h
+++ b/Objects/clinic/bytesobject.c.h
@@ -17,7 +17,7 @@
 "    -1 (the default value) means no limit.");
 
 #define BYTES_SPLIT_METHODDEF    \
-    {"split", (PyCFunction)bytes_split, METH_FASTCALL|METH_KEYWORDS, bytes_split__doc__},
+    {"split", (PyCFunction)(void(*)(void))bytes_split, METH_FASTCALL|METH_KEYWORDS, bytes_split__doc__},
 
 static PyObject *
 bytes_split_impl(PyBytesObject *self, PyObject *sep, Py_ssize_t maxsplit);
@@ -136,7 +136,7 @@
 "Splitting is done starting at the end of the bytes and working to the front.");
 
 #define BYTES_RSPLIT_METHODDEF    \
-    {"rsplit", (PyCFunction)bytes_rsplit, METH_FASTCALL|METH_KEYWORDS, bytes_rsplit__doc__},
+    {"rsplit", (PyCFunction)(void(*)(void))bytes_rsplit, METH_FASTCALL|METH_KEYWORDS, bytes_rsplit__doc__},
 
 static PyObject *
 bytes_rsplit_impl(PyBytesObject *self, PyObject *sep, Py_ssize_t maxsplit);
@@ -184,7 +184,7 @@
 "If the argument is omitted or None, strip leading and trailing ASCII whitespace.");
 
 #define BYTES_STRIP_METHODDEF    \
-    {"strip", (PyCFunction)bytes_strip, METH_FASTCALL, bytes_strip__doc__},
+    {"strip", (PyCFunction)(void(*)(void))bytes_strip, METH_FASTCALL, bytes_strip__doc__},
 
 static PyObject *
 bytes_strip_impl(PyBytesObject *self, PyObject *bytes);
@@ -215,7 +215,7 @@
 "If the argument is omitted or None, strip leading  ASCII whitespace.");
 
 #define BYTES_LSTRIP_METHODDEF    \
-    {"lstrip", (PyCFunction)bytes_lstrip, METH_FASTCALL, bytes_lstrip__doc__},
+    {"lstrip", (PyCFunction)(void(*)(void))bytes_lstrip, METH_FASTCALL, bytes_lstrip__doc__},
 
 static PyObject *
 bytes_lstrip_impl(PyBytesObject *self, PyObject *bytes);
@@ -246,7 +246,7 @@
 "If the argument is omitted or None, strip trailing ASCII whitespace.");
 
 #define BYTES_RSTRIP_METHODDEF    \
-    {"rstrip", (PyCFunction)bytes_rstrip, METH_FASTCALL, bytes_rstrip__doc__},
+    {"rstrip", (PyCFunction)(void(*)(void))bytes_rstrip, METH_FASTCALL, bytes_rstrip__doc__},
 
 static PyObject *
 bytes_rstrip_impl(PyBytesObject *self, PyObject *bytes);
@@ -281,7 +281,7 @@
 "The remaining characters are mapped through the given translation table.");
 
 #define BYTES_TRANSLATE_METHODDEF    \
-    {"translate", (PyCFunction)bytes_translate, METH_FASTCALL|METH_KEYWORDS, bytes_translate__doc__},
+    {"translate", (PyCFunction)(void(*)(void))bytes_translate, METH_FASTCALL|METH_KEYWORDS, bytes_translate__doc__},
 
 static PyObject *
 bytes_translate_impl(PyBytesObject *self, PyObject *table,
@@ -318,7 +318,7 @@
 "The bytes objects frm and to must be of the same length.");
 
 #define BYTES_MAKETRANS_METHODDEF    \
-    {"maketrans", (PyCFunction)bytes_maketrans, METH_FASTCALL|METH_STATIC, bytes_maketrans__doc__},
+    {"maketrans", (PyCFunction)(void(*)(void))bytes_maketrans, METH_FASTCALL|METH_STATIC, bytes_maketrans__doc__},
 
 static PyObject *
 bytes_maketrans_impl(Py_buffer *frm, Py_buffer *to);
@@ -363,7 +363,7 @@
 "replaced.");
 
 #define BYTES_REPLACE_METHODDEF    \
-    {"replace", (PyCFunction)bytes_replace, METH_FASTCALL, bytes_replace__doc__},
+    {"replace", (PyCFunction)(void(*)(void))bytes_replace, METH_FASTCALL, bytes_replace__doc__},
 
 static PyObject *
 bytes_replace_impl(PyBytesObject *self, Py_buffer *old, Py_buffer *new,
@@ -412,7 +412,7 @@
 "    can handle UnicodeDecodeErrors.");
 
 #define BYTES_DECODE_METHODDEF    \
-    {"decode", (PyCFunction)bytes_decode, METH_FASTCALL|METH_KEYWORDS, bytes_decode__doc__},
+    {"decode", (PyCFunction)(void(*)(void))bytes_decode, METH_FASTCALL|METH_KEYWORDS, bytes_decode__doc__},
 
 static PyObject *
 bytes_decode_impl(PyBytesObject *self, const char *encoding,
@@ -447,7 +447,7 @@
 "true.");
 
 #define BYTES_SPLITLINES_METHODDEF    \
-    {"splitlines", (PyCFunction)bytes_splitlines, METH_FASTCALL|METH_KEYWORDS, bytes_splitlines__doc__},
+    {"splitlines", (PyCFunction)(void(*)(void))bytes_splitlines, METH_FASTCALL|METH_KEYWORDS, bytes_splitlines__doc__},
 
 static PyObject *
 bytes_splitlines_impl(PyBytesObject *self, int keepends);
@@ -499,4 +499,4 @@
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=470acd12b2534765 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=07b33ac65362301b input=a9049054013a1b77]*/