omit -Werror (when clang is used)

Index: CMakeLists.txt
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -69,7 +69,7 @@ else(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
   # Use -Werror for clang only.
   if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
     if(NOT CMAKE_CXX_FLAGS MATCHES "-Werror")
-      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror")
+    #set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror")
     endif(NOT CMAKE_CXX_FLAGS MATCHES "-Werror")
   endif(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
 
