Use switch statements in preparation for adding more architectures.

llvm-svn: 199529
diff --git a/clang/lib/Driver/ToolChains.cpp b/clang/lib/Driver/ToolChains.cpp
index 1d32c45..c056346 100644
--- a/clang/lib/Driver/ToolChains.cpp
+++ b/clang/lib/Driver/ToolChains.cpp
@@ -2262,8 +2262,13 @@
   unsigned Major, Minor, Micro;
   getTriple().getOSVersion(Major, Minor, Micro);
   if (Major >= 7 || (Major == 6 && Minor == 99 && Micro >= 23) || Major == 0) {
-    if (getArch() == llvm::Triple::x86 || getArch() == llvm::Triple::x86_64)
+    switch (getArch()) {
+    case llvm::Triple::x86:
+    case llvm::Triple::x86_64:
       return ToolChain::CST_Libcxx;
+    default:
+      break;
+    }
   }
   return ToolChain::CST_Libstdcxx;
 }