WCDH: Fix cxx_nullptr workaround for pre-C++11 compilers

Use just '0' instead of 'static_cast<void*>(0)' because the latter
will not automatically convert to pointers to other types.

Modules/WriteCompilerDetectionHeader.cmake

@@ -586,7 +586,7 @@ function(write_compiler_detection_header
 #  if ${def_name}
 #    define ${def_value} nullptr
 #  else
-#    define ${def_value} static_cast<void*>(0)
+#    define ${def_value} 0
 #  endif
 \n")
       endif()