Dropped self assignment when initialising variables in tokenize.c.

The 'int x=x' style statement do not make sense and cause problems with some compilers. Replace it with 'int x=0' to ensure the value have a well known starting point.

Added -Werror=uninitialized -Winit-self to default GCC build to ensure this style of statement do not sneak into the code again.

Fixes #2317 (closed)