On Linux, we get a compile error because __int64_t is defined and
included by stdint.h. Double underscores are reseved in C in general
and should not be used anyway. Replace with a single leading underscore.
sqrt can now be compiled without 64-bit compiler support.
All remaining functions which aren't supported in 32-bit are now disabled when the FIXMATH_NO_64BIT macro is enable which should stop any compiler errors on compilers where 64-bit isn't supported.
Chris Hammond