+
+@item
+Some platforms provide a @code{NULL} macro that cannot be used in arbitrary
+expressions:
+NetBSD 5.0
+@end itemize
+
+Portability problems fixed by the Gnulib module @code{system-posix}:
+@itemize
+@item
+The macros @code{WIFSIGNALED}, @code{WIFEXITED}, @code{WIFSTOPPED},
+@code{WTERMSIG}, @code{WEXITSTATUS}, @code{WNOHANG}, @code{WUNTRACED},
+@code{WSTOPSIG} are not defined in this header file (only in
+@code{<sys/wait.h>}) on some platforms:
+MirBSD 10.