[PATCH] clang-cl: Implement the -arch flag

[Hans Wennborg]

================
Comment at: lib/Driver/Tools.cpp:1454
@@ +1453,3 @@
+    std::string ArchLower(Arch);
+    std::transform(ArchLower.begin(), ArchLower.end(), ArchLower.begin(), std::tolower);
+    bool ArchUsed = false;
----------------
Hans Wennborg wrote:
> You can just do:
> 
> std::string ArchLower = Arch->lower();
> 
> Or maybe just use Arch->lower() when updating Features in the code below.
And by Arch->lower(), I mean Arch.lower() of course :)

http://reviews.llvm.org/D4519