Add FSGSBASE intrinsics to x86 intrinsic headers.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@221130 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Realphabetize the feature string decoding function since it was mostly in alphabetical order.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@221131 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Add cx16 feature to KNL, SKX, and CoreAVXi CPUs.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@221132 91177308-0d34-0410-b5e6-96231b3b80d8