[CMake] problems when upgrading cmake

[Clinton Stimpson]

I've got this in a CMakeLists.txt file:

PROJECT(foo)
MESSAGE("${CMAKE_SIZEOF_VOID_P}")

If I run with cmake 2.6 it prints out the size.
If I run cmake 2.8 on it without deleting the cache, it goes empty.
If I manually fix CMakeFiles/CMakeC*Compiler.cmake, everything else 
seems fine.

Am I supposed to delete my cache?  Or is cmake not supposed to leave me 
with an empty sizeof void*?

Thanks,
Clint