REORG: compat: move some integer limit definitions from standard.h to compat.h

REORG: compat: move some integer limit definitions from standard.h to compat.h

Historically standard.h was the location where we used to (re-)define the
standard set of macros and functions, and to complement the ones missing
on the target OS. Over time it has become a toolbox in itself relying on
many other things, and its definition of LONGBITS is used everywhere else
(e.g. for MAX_THREADS), resulting in painful circular dependencies.

Let's move these few defines (integer sizes) to compat.h where other
similar definitions normally are.