Single Threaded Builds

Zig has a compile option -fsingle-threaded which has the following effects:

• All Thread Local Variables are treated as regular Container Level Variables.
• The overhead of Async Functions becomes equivalent to function call overhead.
• The @import("builtin").single_threaded becomes true and therefore various userland APIs which read this variable become more efficient. For example std.Mutex becomes an empty data structure and all of its functions become no-ops.