Use __MINGW instead of __MING. Patch contributed by Henrik Bach.

llvm-svn: 16970
diff --git a/llvm/lib/System/Win32/Signals.cpp b/llvm/lib/System/Win32/Signals.cpp
index c1658f9..5c6e008 100644
--- a/llvm/lib/System/Win32/Signals.cpp
+++ b/llvm/lib/System/Win32/Signals.cpp
@@ -16,7 +16,7 @@
 #include <stdio.h>
 #include <vector>
 
-#ifdef __MING
+#ifdef __MINGW
 #include <imagehlp.h>
 #else
 #include <dbghelp.h>