The function gets the real time in useconds and puts it in
a Bit64u. This function is defined when:
BX_HAVE_REALTIME_USEC is 1.
Right now, BX_HAVE_REALTIME_USEC is defined to be BX_HAVE_GETTIMEOFDAY
and bx_get_realtime64_usec is defined in terms of gettimeofday().
However, it could be defined in terms of any other method of obtaining
the current time accurate to the usecond. That is why I moved the
function to osdep and added the new define.
- use Bit64u and other compiler-independent types
- moved contents of macutils.* into osdep.*.
- now in osdep.h, I allow all code to use the real library function name.
If that function is not available, #define it to point to the
bx_* replacement function instead. And cause the bx_* replacement
function to be compiled in osdep.cc.
