portable patch for Class::MOP

=== MOP.xs
==================================================================
--- MOP.xs      (revision 22684)
+++ MOP.xs      (local)
@@ -127,10 +127,11 @@
                             /* BAH! constants are horrible */
                             key = HePV(he, keylen);
                             fqlen = pkglen + keylen + 3;
-                            fq = (char *)alloca(fqlen);
-                            snprintf(fq, fqlen, "%s::%s", package, key);
+                            Newx(fq, fqlen, char);
+                            sprintf(fq, "%s::%s", package, key);
                             sv = (SV*)get_cv(fq, 0);
                             sv_2mortal(sv);
+                            Safefree(fq);
                             break;
                         default:
                             continue;