Creates a child process.
argv[0] is the name of the program to execute. If it is not already a
file path (i.e. it contains '/'), it is resolved into a file path based on
PATH from the parent environment.
pub fn spawn(io: Io, options: SpawnOptions) SpawnError!Child
pub fn spawn(io: Io, options: SpawnOptions) SpawnError!Child {
return io.vtable.processSpawn(io.userdata, options);
}