Go back to using the integrated assembler on windows ever when passed
-no-integrated-as. It is the only assembler we have there.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177398 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/WindowsToolChain.cpp b/lib/Driver/WindowsToolChain.cpp
index b3fdb35..ae78272 100644
--- a/lib/Driver/WindowsToolChain.cpp
+++ b/lib/Driver/WindowsToolChain.cpp
@@ -41,8 +41,9 @@
   case Action::AssembleJobClass:
     if (getTriple().getEnvironment() == llvm::Triple::MachO)
       return new tools::darwin::Assemble(*this);
-    llvm_unreachable("We only have the integrated assembler on this TC");
-    break;
+    // There no assembler we can use on windows other than the integrated
+    // assembler, so we ignore -no-integrated-as.
+    return new tools::ClangAs(*this);
   case Action::LinkJobClass:
     return new tools::visualstudio::Link(*this);
   default: