@itemize
@item
This function is missing on some platforms:
-NetBSD 5.0, Cygwin, mingw, BeOS.
+NetBSD 5.0, Minix 3.1.8, Cygwin, mingw, MSVC 9, BeOS.
+@item
+This function is not declared in @code{<unistd.h>}
+(without @code{-D_GNU_SOURCE}) on some platforms:
+glibc (at least 2.11–2.13).
@end itemize