New module 'getrusage'.

New module 'getrusage'.

* lib/sys_resource.in.h: Include arg-nonnull.h, c++defs.h,
warn-on-use.h.
(getrusage): New declaration.
* lib/getrusage.c: New file.
* m4/getrusage.m4: New file.
* m4/sys_resource_h.m4 (gl_HEADER_SYS_RESOURCE): Test whether getrusage
is declared.
(gl_SYS_RESOURCE_H_DEFAULTS): Initialize GNULIB_GETRUSAGE,
HAVE_GETRUSAGE.
* modules/sys_resource (Depends-on): Add snippet/arg-nonnull,
snippet/c++defs, snippet/warn-on-use.
(Makefile.am): Update generation of sys/resource.h. Substitute
GNULIB_GETRUSAGE, HAVE_GETRUSAGE.
* modules/getrusage: New file.
* doc/posix-functions/getrusage.texi: Mention the new module.