stdlib: don't depend on stdint

stdlib: don't depend on stdint

* lib/stdlib.in.h: Don't include <stdint.h> merely because
GNULIB_POSIXCHECK is defined.  GNULIB_POSIXCHECK seems to
be independent of whether stdint.h is needed.
* m4/random_r.m4 (gl_FUNC_RANDOM_R): Check for struct random_data
here, instead of ...
* m4/stdlib_h.m4 (gl_STDLIB_H): ... here.  Applications that need
struct random_data should be using the random_r module, not just
the stdlib module (which wouldn't make sense: what package needs
just struct random_data without also needing random_r?).
* modules/stdlib (Depends-on): Remove stdint.