This header file is missing on some platforms:
Minix 3.1.8, mingw, MSVC 9, BeOS.
@item
+This header file does not define the type @code{pid_t} on some platforms:
+glibc 2.11, MacOS X 10.5.
+@item
@code{struct sched_param} is not defined on some platforms:
Haiku.
@item