add missing std lib file rb.zig to cmakelists.txt
add missing std lib file rb.zig to cmakelists.txt

raulgrell/zig,zig-lang/zig,raulgrell/zig,andrewrk/zig,raulgrell/zig,andrewrk/zig,zig-lang/zig,zig-lang/zig,raulgrell/zig,raulgrell/zig