On linux Which lib provides the directRDP function?
There is no library. That's all Linux-#ifdef'd code. But given that the implementation section is referencing for instance the SessionWidget::directRDP(bool, bool) signal, it should work.
From the excerpt you've shown, I have no idea what you invoked and how so. I also have no idea if the moc binary has been executed on relevant source files and generated metaobjects code. If possible, please always paste *everything*, not just the part that you may deem interesting.
Build log from "make V=1" attached.
There was a bug in the source code in the sense that it did connect two unavailable signals on non-Linux platforms.
In your case, I observe that:
*Why* are you not using the Qt version as provided by your package manager? Why are you rolling your own solution, if you are incapable of debugging and handling such issues yourself?
The path /tmp/tcloop/qt-4.x-dev/usr/local/share/qt4/mkspecs/linux-g++ might not even exist any longer. Who knows what compiler spec qmake falls back to.
I fixed the issue I found in x2goclient via https://code.x2go.org/gitweb?p=x2goclient.git;a=commitdiff;h=1f383a9029ba1d1...
This likely won't help you, though, since the definitions as seen by your meta object compiler (moc) and C++ compiler (g++) still won't match up.
Package maintainers normally go a great length to make sure that the packages they build work correctly and handle bug reports. Subverting this by rolling your own version is not as smart an idea as you might think it is.
Looking around, you seem to be using tinycorelinux, which stages non-core software to /usr/local. That hints that it was installed there by a package manager, but doesn't explain why qmake is trying to read spec files from /tmp/tcloop/qt-4.x-dev. There's definitely something odd with your system or the way these packages have been built.
Sorry, this is not a problem X2Go Client, but rather with your Qt libraries.
Mihai