qt5base-lts/mkspecs/features/qt_build_paths.prf

# Find the module's source root dir.
MODULE_PROFILE_DIR = $$_PRO_FILE_PWD_
for(ever) {
    exists($$MODULE_PROFILE_DIR/sync.profile):break()
    nmpri = $$dirname(MODULE_PROFILE_DIR)
    equals(nmpri, $$MODULE_PROFILE_DIR):error("No sync.profile found. This does not look like a Qt module source tree.")
    MODULE_PROFILE_DIR = $$nmpri
    unset(nmpri)
}

isEmpty(MODULE_BASE_DIR): MODULE_BASE_DIR = $$MODULE_PROFILE_DIR
isEmpty(MODULE_BASE_OUTDIR): MODULE_BASE_OUTDIR = $$shadowed($$MODULE_BASE_DIR)
isEmpty(MODULE_QMAKE_OUTDIR): MODULE_QMAKE_OUTDIR = $$MODULE_BASE_OUTDIR

QTDIR = $$[QT_HOST_PREFIX]
exists($$QTDIR/.qmake.cache) {
    # Permit modules to enforce being built outside QTDIR ...
    !force_independent: MODULE_BASE_OUTDIR = $$QTDIR
    # ... though this sort of breaks the idea.
    MODULE_QMAKE_OUTDIR = $$QTDIR
}