Rename Darwin_X86 toolchain to just Darwin, this can support all platforms.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@81016 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/Tools.h b/lib/Driver/Tools.h
index 67e25f6..4821c54 100644
--- a/lib/Driver/Tools.h
+++ b/lib/Driver/Tools.h
@@ -21,7 +21,7 @@
   class Driver;
 
 namespace toolchains {
-  class Darwin_X86;
+  class Darwin;
 }
 
 namespace tools {
@@ -201,7 +201,9 @@
     void AddDarwinSubArch(const ArgList &Args, ArgStringList &CmdArgs) const;
     void AddLinkArgs(const ArgList &Args, ArgStringList &CmdArgs) const;
 
-    const toolchains::Darwin_X86 &getDarwinToolChain() const;
+    const toolchains::Darwin &getDarwinToolChain() const {
+      return reinterpret_cast<const toolchains::Darwin&>(getToolChain());
+    }
 
   public:
     Link(const ToolChain &TC)