Fix invalid acl_entry_t on 32-bit Cygwin

If the acl_t struct was at or above 0x80000000 then the pointer was
sign-extended to 0xffff_ffff_8000_0000 and so the index was lost.

Signed-off-by: David Allsopp <david.allsopp@metastack.com>

winsup/cygwin/release/3.1.7

@@ -0,0 +1,4 @@
+Bug Fixes:
+----------
+
+- Fix acl_get_* functions in 32-bit Cygwin (pointer sign extension)

winsup/cygwin/sec_posixacl.h

@@ -34,7 +34,7 @@ struct __acl_t
 inline acl_entry_t
 __to_entry (acl_t acl, uint16_t idx)
 {
-  return ((uint64_t) idx << 48) | (uint64_t) acl;
+  return ((uint64_t) idx << 48) | (uint64_t) ((uintptr_t) acl);
 }
 #define __to_permset(a,i)	((acl_permset_t)__to_entry((a),(i)))