depends: Do not set build_subdir for qt package
This change makes the next commit possible without exporting the PATH
variable.
depends: Use more legible qmake commands in qt package
This change gets rid of multiple ../ that makes reasoning about the
script and its maintaining much easier.Co-authored-by: fanquake <fanquake@gmail.com>
See D830 for the differences in the source material.
This is a backport of core#20673
Depends on D13664