clean up error return tracing

* error return tracing is disabled in release-fast mode
 * add @errorReturnTrace
 * zig build API changes build return type from `void` to `%void`
 * allow `void`, `noreturn`, and `u8` from main. closes #535
7b57454cc1Andrew Kelley committed on 1/15/2018, 5:01:02 AMparentd973b40
22 files changedLine totals unavailable