Portability to non C99 compliant compilers

OS400 C compiler is not C99 compliant.
It only supports local variable declarations at the beginning of a block.
We loose the const as a result but portability is more important.
diff --git a/xmlschemastypes.c b/xmlschemastypes.c
index 60f5414..5f38599 100644
--- a/xmlschemastypes.c
+++ b/xmlschemastypes.c
@@ -5307,6 +5307,7 @@
 			       xmlSchemaWhitespaceValueType ws)
 {
     int ret;
+    int stringType;
 
     if (facet == NULL)
 	return(-1);
@@ -5324,8 +5325,8 @@
 	    * the datatype.
 	    * See https://www.w3.org/TR/xmlschema-2/#rf-pattern
 	    */
-	    const int stringType = val && ((val->type >= XML_SCHEMAS_STRING && val->type <= XML_SCHEMAS_NORMSTRING)
-	                                    || (val->type >= XML_SCHEMAS_TOKEN && val->type <= XML_SCHEMAS_NCNAME));
+	    stringType = val && ((val->type >= XML_SCHEMAS_STRING && val->type <= XML_SCHEMAS_NORMSTRING)
+			      || (val->type >= XML_SCHEMAS_TOKEN && val->type <= XML_SCHEMAS_NCNAME));
 	    ret = xmlRegexpExec(facet->regexp,
 	                        (stringType && val->value.str) ? val->value.str : value);
 	    if (ret == 1)