Enable pointer TBAA for LTO

[Jan Hubicka]

> 
> I think it also causes the following and one related ICE
> 
> FAIL: gcc.dg/vect/pr62021.c -flto -ffat-lto-objects (internal compiler 
> error)
> 
> /space/rguenther/src/svn/trunk3/gcc/testsuite/gcc.dg/vect/pr62021.c:7:1: 
> internal compiler error: in get_alias_set, at alias.c:880^M
> 0x7528a7 get_alias_set(tree_node*)^M
>         /space/rguenther/src/svn/trunk3/gcc/alias.c:880^M

Does this one reproduce with mainline? All thee ICEs are on the sanity check:
gcc_checking_assert (!in_lto_p || !type_with_alias_set_p (t));
which check that in LTO all types that ought to have CANONICAL_TYPE gets CANONICAL_TYPE
computed.  ICE here probalby means that the type somehow bypassed LTO canonical type merging
as well as the TYPE_CANONICAL=MAIN_VARIANT set in lto-streamer.c

Honza