base: use uintptr_t for hash type

Use uintptr_t for hash type; this is consistent with CoreFoundation, which uses
32-bit integers on 32-bit platforms for the hash code, and 64-bit integers on
64-bit platforms. (libheimbase is modelled on CoreFoundation.)

Previously we used unsigned long, which would have the same behavior on
LP32/LP64 systems, but not on Windows (where unsigned long is 32-bits on 64-bit
platforms).

lib/base/error.c

@@ -58,7 +58,7 @@ error_cmp(void *a, void *b)
     return heim_cmp(ap->msg, bp->msg);
 }
 
-static unsigned long
+static uintptr_t
 error_hash(void *ptr)
 {
     struct heim_error *p = ptr;