Conflicts:
 * lib/std/zig/ast.zig
 * lib/std/zig/parse.zig
 * lib/std/zig/parser_test.zig
 * lib/std/zig/render.zig
 * src/Module.zig
 * src/zir.zig

I resolved some of the conflicts by reverting a small portion of
@tadeokondrak's stage2 logic here regarding `callconv(.Inline)`.
It will need to get reworked as part of this branch.