Shadow build directory relative to the project file?

[Foul Ole Ron]

I had the same problem, and although 'Guru' wysota is - of course - right, I did find a *workable* solution for a newbie (like me).

You can edit the .pro file, and add the following lines:

OBJECTS_DIR=$$builddir
DESTDIR=$$builddir

I tested this with a lib build. This will make sure that the binaries will go into the ./release and ./debug directories respectively (if nothing else edited).

Another option is to set these variables conditionally in the .pro file:
win32: { DESTDIR = dir1 }
linux: { DESTDIR = dir1 }
...