Update to splay-tree.h for 64-bit Windows host

[Ian Lance Taylor]

Nick Clifton <nickc@redhat.com> writes:

> +#ifndef _WIN64
> +  typedef unsigned long int libi_uhostptr_t;
> +  typedef long int libi_shostptr_t;
> +#else
> +  typedef unsigned long long libi_uhostptr_t;
> +  typedef long long libi_shostptr_t;
> +#endif

I think we should instead use a configure test to see whether
<stdint.h> exists and defines uintptr_t and intptr_t.  We should use
those when they exist.  If they don't, we should do something like

#ifdef __GNUC__
typedef unsigned int libi_uhostptr_t __attribute__ ((mode (pointer)));
typedef int libi_shostptr_t __attribute__ ((mode (pointer)));
#else
typedef unsigned long long libi_uhostptr_t;
typedef long long libi_shostptr_t;
#endif

Ideally we don't have to test _WIN64 at all.

Ian