Makefile-based generators of CMake are much less efficient than Ninja. They
generate bloated Makefiles that call back to cmake often. Main offender on
Windows is cmake_depends command which seems to do lots of disk reads.
QtWebKit can now switch to ninja automatically if it's present in PATH.
This should help to reduce build times.
Change-Id: I33d3f4d766a630f8ca4fb64b719fe2e8a5c2e00c
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>