POSIX specification:
http://www.opengroup.org/onlinepubs/9699919799/basedefs/stdlib.h.html
Gnulib module: stdlib, system-posix
Portability problems fixed by the Gnulib module stdlib:
EXIT_SUCCESS and EXIT_FAILURE are not defined on
some platforms.
EXIT_FAILURE is incorrectly defined on Tandem/NSK.
NULL macro that cannot be used in arbitrary
expressions:
NetBSD 5.0
Portability problems fixed by the Gnulib module system-posix:
WIFSIGNALED, WIFEXITED, WIFSTOPPED,
WTERMSIG, WEXITSTATUS, WNOHANG, WUNTRACED,
WSTOPSIG are not defined in this header file (only in
<sys/wait.h>) on some platforms:
MirBSD 10.
Portability problems not fixed by Gnulib:
WEXITSTATUS require an lvalue
argument on some platforms.
Mac OS X 10.5.