PCH dependency not added for generated moc_*.cpp files

Enabling precompiled header in a project where some header files need to be moc'ed causes a build failure because the new build rules dynamically added for app -> moc_x.o -> moc_x.cpp -> x.h lack a moc_x.o -> pch_output dependency.

This usually results in moc_x.cpp files being compiled before/during pch compilation (depending whether doing -j1 or a parallel build), thus resulting in either:

1) moc_x.cpp compilation failing due to missing PCH
2) moc_x.cpp compilation failing due to invalid PCH

In addition, the graph output by "qbs graph" for the same project is very different in the 3 following cases:

1) $ qbs clean && qbs graph # Graph OK, moc rules not yet present.
2) $ qbs clean && qbs -j1; qbs graph # New moc rules miss dependency on PCH
3) $ qbs clean && qbs -j8; qbs graph # ALL .o -> .cpp rules miss dependency on PCH

I have attached a small project that show all those issues.