* See #204 - zig build system
* allow builtin types Os, Environ, Arch to be used at runtime.
they have zero_bits=false and debug info now.
* Eradicate use of `@alloca` in std for syscalls. See #225
* add `std.io.writeFile`
* `std.debug.panic` adds a newline to format
* introduce zigrt file. it contains only weak symbols so that
multiple instances can be merged. it contains __zig_panic
so that multiple .o files can call the same panic function.
* remove `@setFnVisible` builtin and add @setGlobalLinkage builtin
which is more powerful
* add `@panic` builtin function.
* fix collision of symbols with extern prototypes and internal
function names
* add stack protector safety when linking against libc. To add
the safety mechanism without libc requires implementing
Thread Local Storage. See #276
