Extra compilers with "CONFIG += combine" were broken for qmake's vcxproj
generator since forever.
Usually, extra compilers are handled by attaching the Custom Build Tool
to the input file. This is not possible for combine extra compilers,
because they map multiple inputs to one output. We cannot attach the
Custom Build Tool to the output either, because this would result in
circular dependency errors (output trying to create output itself).
To fix this, we create a custom build tool fake file (.cbt) for the
output and attach the Custom Build Tool there. This is the same trick
we do for regular extra compilers that have C++ sources as
input (e.g. the one that generates moc_predefs.h).
Pick-to: 6.2 5.15
Fixes: QTBUG-94806
Change-Id: Ib808a43fead737df91b89a1ac5e180aeae37efae
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
e022ff0a8e