Summary:
Turns out that swapping stdout and stderr using a temporary fd 3 was screwing
up with make's jobserver, who also uses fd 3!
Also, infer is partly to blame as it also calls `make`. Unsetting `MAKEFLAGS`
in infer tells `make` that the way infer calls `make` is independent from
parent `make` invocations.
Also, simplify the rules for direct tests and build system tests.
Reviewed By: jberdine
Differential Revision: D4328979
fbshipit-source-id: 96818e8
Jules Villard