Centralize the logic for using the integrated assembler.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177360 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/WindowsToolChain.cpp b/lib/Driver/WindowsToolChain.cpp
index 985039e..0909c4c 100644
--- a/lib/Driver/WindowsToolChain.cpp
+++ b/lib/Driver/WindowsToolChain.cpp
@@ -50,11 +50,9 @@
   case Action::CompileJobClass:
     return new tools::Clang(*this);
   case Action::AssembleJobClass:
-    if (!useIntegratedAs() &&
-        getTriple().getEnvironment() == llvm::Triple::MachO)
+    if (getTriple().getEnvironment() == llvm::Triple::MachO)
       return new tools::darwin::Assemble(*this);
-    else
-      return new tools::ClangAs(*this);
+    llvm_unreachable("We only have the integrated assembler on this TC");
     break;
   case Action::LinkJobClass:
     return new tools::visualstudio::Link(*this);