Fix LLVM's handling and detection of skylake and cannonlake CPUs

Summary:
 - Rename `"skylake"` == SkylakeServerProc to `"skylake-avx512"`
 - Change `"skylake"` to denote SkylakeClientProc
 - Fix the detection of cpu family 6 and model 94 to be
   SkylakeClientProc instead of SkylakeServerProc
 - Remove the `"cnl"` for CannonLake

Reviewers: craig.topper, delena

Subscribers: zansari, echristo, qcolombet, RKSimon, spatel, DavidKreitzer, mcrosier, llvm-commits

Differential Revision: http://reviews.llvm.org/D17090

llvm-svn: 261482
diff --git a/llvm/lib/Support/Host.cpp b/llvm/lib/Support/Host.cpp
index ffad1d7..1ca8eac 100644
--- a/llvm/lib/Support/Host.cpp
+++ b/llvm/lib/Support/Host.cpp
@@ -373,6 +373,7 @@
 
       // Skylake:
       case 78:
+        return "skylake-avx512";
       case 94:
         return "skylake";