C++ const fix in test

tests/run/arithmetic_analyse_types_helper.h

 /* A set of mutually incompatable return types. */
 
-struct short_return { const char *msg; };
-struct int_return { const char *msg; };
-struct longlong_return { const char *msg; };
+struct short_return { char *msg; };
+struct int_return { char *msg; };
+struct longlong_return { char *msg; };
 
 /* A set of overloaded methods. */
 
 short_return f(short arg) {
     short_return val;
-    val.msg = "short called";
+    val.msg = (char*)"short called";
     return val;
 }
 
 int_return f(int arg) {
     int_return val;
-    val.msg = "int called";
+    val.msg = (char*)"int called";
     return val;
 }
 
 longlong_return f(long long arg) {
     longlong_return val;
-    val.msg = "long long called";
+    val.msg = (char*)"long long called";
     return val;
 }