add missing iso646 header
handle VA_COPY destination in mark_vars_read()
infrastructure to set __OPTIMIZE__ and __OPTIMIZE_SIZE__ predefs

Unfortunately we can't enable this yet (see comment in source)
remove old+unused typedef
refactor builtins, add support for libc function matching

- We can now detect known libc functions and replace them with more
  performant builtins.
- Implement cimag* and creal* from C99 with this infrastructure
remove support for ms try/leave

We didn't have code generation for them anyway.