[X86] Add a /tune: option for clang-cl

We recently added support for -mtune. This patch adds /tune: so we can specify the tune CPU from clang-cl. MSVC doesn't support this but icc does.

Differential Revision: https://reviews.llvm.org/D86820

Author: topperc

clang/include/clang/Driver/Options.td

@@ -4696,6 +4696,9 @@ def _SLASH_openmp : CLFlag<"openmp">, HelpText<"Enable OpenMP support">,
 def _SLASH_openmp_experimental : CLFlag<"openmp:experimental">,
   HelpText<"Enable OpenMP support with experimental SIMD support">,
   Alias<fopenmp>;
+def _SLASH_tune : CLCompileJoined<"tune:">,
+  HelpText<"Set CPU for optimization without affecting instruction set">,
+  Alias<mtune_EQ>;
 
 // Non-aliases:
 

clang/test/Driver/cl-x86-flags.c

@@ -128,5 +128,9 @@
 // RUN: %clang_cl -m64 -arch:avx512 --target=i386-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=avx51264 %s
 // avx51264: argument unused during compilation
 
+// RUN: %clang_cl -m64 -arch:AVX -tune:haswell --target=x86_64-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=tune %s
+// tune: "-target-cpu" "sandybridge"
+// tune-SAME: "-tune-cpu" "haswell"
+
 void f() {
 }