devchk: stdlib_h.c checks internal drand48_data struct members

[Matt Wilson <msw@redhat.com>]

the drand48_data structure in stdlib.h should be considered an opaque
type.  Checking the sizeof() should be sufficient for compatibility.

>From the header:

/* Data structure for communication with thread safe versions.  This
   type is to be regarded as opaque.  It's only exported because users
   have to allocate objects of this type.  */

Cheers,

Matt