The forwarding header is left in place because of its use in
`polly/lib/External/isl/interface/extract_interface.cc`, but I have
added a GCC warning about the fact it is deprecated, because it is used
in `isl` from where it is included by Polly.
Add a new lit-cpuid tool that detects CPU features used by some of
the tests, and use it to populate available_features in lit. For now,
this means that the test for MM/XMM register read will be run only
when the host CPU support SSE instruction set. However, this is going
to make it possible to introduce additional tests relying on AVX.
Differential Revision: https://reviews.llvm.org/D61073
llvm-svn: 359303
