This function is missing on some platforms. However, the replacement
is designed to be lightweight, and may round to the neareset second;
use @code{select} or @code{nanosleep} if better resolution is needed:
-IRIX 5.3, Solaris 2.4, older mingw, BeOS.
+IRIX 5.3, Solaris 2.4, older mingw, MSVC 9, BeOS.
@end itemize
Portability problems not fixed by Gnulib: