Compile with Ninja. Ninja compiles faster and is more stable with
parallel builds. Routines copied from cmake.mk.
Speed improves from:
Executed in 127.47 secs fish external
usr time 17.02 mins 446.00 micros 17.02 mins
sys time 1.18 mins 40.00 micros 1.18 mins
to:
Executed in 118.91 secs fish external
usr time 17.28 mins 499.00 micros 17.28 mins
sys time 1.13 mins 45.00 micros 1.13 mins
Signed-off-by: Rosen Penev <rosenp@gmail.com>