assert -> gcc_assert

Hi, GCC 4.0.0 and up use gcc_assert and gcc_unreachable for assertions and unreachable code. This patch updates gpc's assert to be gcc_assert and gcc_unreachable and have the same sematics as the upstream assertion functions. This along with the other patch was built and tested against gcc 3.3 cvs on ia64-linux. -- Thanks, Jim http://phython.blogspot.com