lupdate and lrelease ignore conditionals in qmake project files

lupdate and lrelease ignore conditionals in qmake project files.

TEMPLATE = app
SOURCES += main.cpp
TRANSLATIONS = lr_fr.ts
win32 {
    QT += nonsense
}

Building on a Linux host, this results in the following output:

WARNING: Project ERROR: Unknown module(s) in QT: nonsense

Extraction and conversion of translation strings is not aborted.