Another windows build fix attempt.

Inspired by http://public.kitware.com/pipermail/cmake-developers/2012-March/003768.html

llvm-svn: 198153
diff --git a/llvm/cmake/modules/AddLLVM.cmake b/llvm/cmake/modules/AddLLVM.cmake
index 6bfed69..404bc38 100644
--- a/llvm/cmake/modules/AddLLVM.cmake
+++ b/llvm/cmake/modules/AddLLVM.cmake
@@ -45,7 +45,7 @@
       VERBATIM
       COMMENT "Creating export file for ${target_name}")
     set_property(TARGET ${target_name} APPEND_STRING PROPERTY
-                 LINK_FLAGS " ${CMAKE_CURRENT_BINARY_DIR}/symbol.def")
+                 LINK_FLAGS "/DEF:${CMAKE_CURRENT_BINARY_DIR}/symbol.def")
   endif()
 
   add_custom_target(${target_name}_exports DEPENDS ${native_export_file})