[AVR] Add -mmcu option to the driver

A patch by Peter Wu!

Reviewers: jroelofs, xiangzhai

Reviewed By: jroelofs, dylanmckay, xiangzhai

Subscribers: dlj, dylanmckay, cfe-commits

Differential Revision: https://reviews.llvm.org/D29827

llvm-svn: 300818
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index cb27330..93b66eb 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -261,6 +261,12 @@
     arm::getARMArchCPUFromArgs(Args, MArch, MCPU, FromAs);
     return arm::getARMTargetCPU(MCPU, MArch, T);
   }
+
+  case llvm::Triple::avr:
+    if (const Arg *A = Args.getLastArg(options::OPT_mmcu_EQ))
+      return A->getValue();
+    return "";
+
   case llvm::Triple::mips:
   case llvm::Triple::mipsel:
   case llvm::Triple::mips64: