[3.5] bpo-32563: Get expat to compile under C89 (#5201)

* [3.5] bpo-32563: Get expat to compile under C89

expat: Add artificial scopes in xmltok.c utf8_toUtf8() to fix c89 compilation.

Cherry-picked from libexpat commit e0b290eb3d8f4c4b45137a7d7f4f8db812145bd2

* Backport XML RPC test skip to 3.5

The buildbot service upgrade removed the XML-RPC
interface, so this test no longer works (through no
fault of the standard library).

* Don't configure a nonexistent Python

Modules/expat/xmltok.c

@@ -405,16 +405,20 @@ utf8_toUtf8(const ENCODING *UNUSED_P(enc),
   }
 
   /* Avoid copying partial characters (from incomplete input). */
-  const char * const fromLimBefore = fromLim;
-  align_limit_to_full_utf8_characters(*fromP, &fromLim);
-  if (fromLim < fromLimBefore) {
-    input_incomplete = true;
+  {
+    const char * const fromLimBefore = fromLim;
+    align_limit_to_full_utf8_characters(*fromP, &fromLim);
+    if (fromLim < fromLimBefore) {
+      input_incomplete = true;
+    }
   }
 
-  const ptrdiff_t bytesToCopy = fromLim - *fromP;
-  memcpy((void *)*toP, (const void *)*fromP, (size_t)bytesToCopy);
-  *fromP += bytesToCopy;
-  *toP += bytesToCopy;
+  {
+    const ptrdiff_t bytesToCopy = fromLim - *fromP;
+    memcpy((void *)*toP, (const void *)*fromP, (size_t)bytesToCopy);
+    *fromP += bytesToCopy;
+    *toP += bytesToCopy;
+  }
 
   if (output_exhausted)  // needs to go first
     return XML_CONVERT_OUTPUT_EXHAUSTED;