Android: make install in qttools fails because of install path

When building Qt for Android configured with "-prefix ..." and "-make tools", "make install" does not use the given prefix for qttools which are built for the target system (Qt Assistant etc.). Instead it tries to install them to $(INSTALL_ROOT)/libs/$$ANDROID_TARGET_ARCH/. This leads to failure for an unprivileged user and empty INSTALL_ROOT.

I would expect to see these binaries (.so) installed to the same prefix as the other target binaries.

(Note: This configuration works in cross-development for Windows on Linux and allows to build Qt Assistant for later deployment to Windows.)

My analysis:

• The non-standard target install path comes from mkspecs/features/android, if !android_app && android_install.
• mkspecs/android-g++/qmake.conf does not set android_app but android_install.
• android_app is set in mkspecs/features/java.prf and in mkspecs/unsupported/android-g++/qmake.conf [!].

I guess these mkspecs result in the intented behaviour when deploying apps which use Qt but they misbehave when installing apps which are part of Qt.

Either this should be fixed, or these tools should not be build/installed for Android.