CMake: fix Ninja's decreasing progress report

Ninja should report completed against overall edges,
this way 100% would only be reached when ninja exits.

Task-number: QTCREATORBUG-10332
Change-Id: I90804db566662b2a96f9ce85b7fab5e1455831c7
Reviewed-by: Daniel Teske <daniel.teske@digia.com>