#68: env.h: include intrin.h when using MSVC++
#68: env.h: include intrin.h when using MSVC++

When compiling with MSVC++ on a little-endian machine, include intrin.h
before using `_byteswap_uint64`, or that macro will be left undefined
and assumed by the compiler to return an int (which is generally
32-bit).

aklomp/base64,htot/base64,aklomp/base64,aklomp/base64,htot/base64,htot/base64