In speed test, check for availability of NIST reducer functions
In speed test, check for availability of NIST reducer functions

This caused compilation to fail if MP_WORD_BITS was 8 or 16

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