Add AVX-512 feature flag and knl cpu to clang.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188758 91177308-0d34-0410-b5e6-96231b3b80d8
[autotools->cmake] Added support for creating the clang driver plist for OS X.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188759 91177308-0d34-0410-b5e6-96231b3b80d8