Extended symbol tables properly handle macros.

Functions do not yet work and is my next area of investigation.
Explicitly set type ref to null in gen_op
Ensure local CType var has null ref null, to avoid confusion elsewhere
More rigorous TokenSym pointer handling for libtcc.h
Update tests to use TokenSym_p
Renamed function sharing test
Cleanup tccpp.c
Renamed _sym_looks_weird -> _sym_is_all_zeros
Minor cleanups in libtcc.h
Add better extended symbol token field handling
Test preprocessor sharing
Get preprocessor token symbol sharing to work
Add struct sharing test
Added debugging symbols for exsymtab test compiling on Mac
Added test output files to ignore list
Tracking down struct member token issues
Hypothesis: Does a TokenSym get copied for "x"?
Conclusion: a TokenSym for "x" is copied
Hypothesis: is lookup_by_name broken, or simply not called, for "x"?
Conclusion: lookup_by_name is called for "x"; must be broken