minor fix to backw compat

Modules/CheckTypeSize.cmake

@@ -7,6 +7,7 @@
 #
 
 MACRO(CHECK_TYPE_SIZE TYPE VARIABLE)
+  SET(CMAKE_ALLOW_UNKNOWN_VARIABLE_READ_ACCESS 1)
   IF("${VARIABLE}" MATCHES "^${VARIABLE}$")
     SET(MACRO_CHECK_TYPE_SIZE_FLAGS 
 	"-DCHECK_TYPE_SIZE_TYPE=\"${TYPE}\" ${CMAKE_REQUIRED_FLAGS}")
@@ -37,4 +38,5 @@ MACRO(CHECK_TYPE_SIZE TYPE VARIABLE)
         APPEND)
     ENDIF(HAVE_${VARIABLE})
   ENDIF("${VARIABLE}" MATCHES "^${VARIABLE}$")
+  SET(CMAKE_ALLOW_UNKNOWN_VARIABLE_READ_ACCESS )
 ENDMACRO(CHECK_TYPE_SIZE)