spawn() results in valgrind warnings

[HildarTheDorf]

TaskBuilder::spawn() is causing a "conditional jump or move depends on uninitialized values(s)" error in valgrind.

fn main() { spawn(proc() {}) }
Is the absolute minimum required to reproduce, and the error message is still present if a TaskBuilder is created and TaskBuilder::spawn() is called directly. Tested on 18c451f (most recent master as of this post).

[thestinger]

This is likely just the same false positive as #11710.

[HildarTheDorf]

Looks like it. Sorry for the duplicate.