tools/cmake: update to 3.20.3 + build with Ninja

tools/cmake: update to 3.20.3 + build with Ninja

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>