QtWebEngine ignores ninja flag for parallel jobs (-j)

qtwebengine seems to always default to the number of cpu cores for the j flag, instead of using the number supplied by the flag.

Example:

bitbake qtwebengine -c devshell
cd ../build
ninja -j 1 # now #cpu-cores jobs are spawned

This very often yields out-of-memorys errors due to the high cpu count on our build server. It also ignores the bitbake PARALLEL_MAKE variable.

ninja version: 1.10.2

yocto version: kirkstone