Skip using mmap allocation if mlock is not available.
Skip using mmap allocation if mlock is not available.

Previously this would just mmap but pointlessly as the memory was
not locked; might as well use the standard heap in that case.

webmaster128/botan,webmaster128/botan,randombit/botan,webmaster128/botan,webmaster128/botan,randombit/botan,randombit/botan,randombit/botan,randombit/botan,webmaster128/botan