Overriding standard type names has no effect if the type was already used
Adapted from Chiong on python-cffi:
#!python
>>> import cffi
>>> ffi=cffi.FFI()
>>> ffi.sizeof("size_t")
8
>>> ffi.cdef("typedef char size_t;")
>>> ffi.sizeof("size_t")
8
>>> ffi=cffi.FFI()
>>> ffi.cdef("typedef char size_t;")
>>> ffi.sizeof("size_t")
1