InstCombine: Convert some tests to opaque pointers

Needed manual fixes:
  2008-01-06-VoidCast.ll
  alias.ll @0 type lost
  pr27703.ll totally confused
  pr44242.ll phi and update_test_checks
  pr44245.ll phi and update_test_checks

Needed re-running update_test_checks:
  2009-01-08-AlignAlloca.ll
  2009-02-20-InstCombine-SROA.ll
  addrspacecast.ll
  alloca-cast-debuginfo.ll
  alloca-in-non-alloca-as.ll
  alloca.ll
  icmp-gep.ll
  icmp-custom-dl.ll
  lifetime-no-null-opt.ll
  non-integral-pointers.ll
  pr33689_same_bitwidth.ll
  pr39908.ll
  scalable-cast-of-alloc.ll
  select-cmp-br.ll
  unpack-fca.ll

Converted to generated checks:
  2012-6-7-vselect-bitcast.ll