Index: cfe/trunk/lib/Basic/Targets/ARM.cpp
===================================================================
--- cfe/trunk/lib/Basic/Targets/ARM.cpp
+++ cfe/trunk/lib/Basic/Targets/ARM.cpp
@@ -1002,6 +1002,7 @@
   DefineStd(Builder, "WIN32", Opts);
   DefineStd(Builder, "WINNT", Opts);
   Builder.defineMacro("_ARM_");
+  Builder.defineMacro("__ARM_DWARF_EH__");
   addMinGWDefines(Opts, Builder);
 }
 
Index: cfe/trunk/test/Preprocessor/init.c
===================================================================
--- cfe/trunk/test/Preprocessor/init.c
+++ cfe/trunk/test/Preprocessor/init.c
@@ -2645,6 +2645,10 @@
 // Thumbebv7: #define __THUMB_INTERWORK__ 1
 // Thumbebv7: #define __thumb2__ 1
 
+// RUN: %clang -E -dM -ffreestanding -target thumbv7-pc-mingw32 %s -o - | FileCheck -match-full-lines -check-prefix THUMB-MINGW %s
+
+// THUMB-MINGW:#define __ARM_DWARF_EH__ 1
+
 //
 // RUN: %clang_cc1 -E -dM -ffreestanding -triple=i386-none-none < /dev/null | FileCheck -match-full-lines -check-prefix I386 %s
 //