A macro is used to control whether struct timespec is declared, because GNO might want to declare it in other headers, and this would allow it to avoid duplicate declarations. (This will still require changes in the GNO headers. Currently, they declare struct timespec with different field names, although the layout is the same.)
Previously, they were hard-coded as 60, but the clock tick frequency actually depends on the video mode. They now call a new library function that can detect the video mode and return the proper value.
This also makes CLOCKS_PER_SEC have the type clock_t, as C99 and later require.
