fix allowing casts of AS pointers to uintptr_t

The patch b3daa62b5 ("also accept casts of AS pointers to uintptr_t")
is bogus and allows uintptr_t as the *source type* instead of the
*target type*. This was helped by a previous bug, in patch
d96da358c ("stricter warning for explicit cast to ulong"), where
a test for Wcast_from_as was wrongly added for the source type.

Fix this by:
* adding the test for uintptr_t to the target type;
* removing the test for Wcast_from_as from the source type,
  replacing it by a test of Wcast_to_as;
* clarify and extend the tge testcases.
So, now, casts from uintptr_t to AS pointers are also allowed.

Fixes: b3daa62b53109dba78c7937b3a6a0cd7d67865d5
Fixes: d96da358cfa0432f067a4e66940765883b80ee62
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
7 files changed