[X86] Add support for more than 32 features for __builtin_cpu_is

libgcc supports more than 32 features by adding a new 32-bit variable __cpu_features2.

This adds the clang support for checking these feature bits.

Patches for compiler-rt and llvm to support this are coming as well.

Probably still need an additional patch for target multiversioning in clang.

Differential Revision: https://reviews.llvm.org/D53458

llvm-svn: 344832