Introduce $$QTC_PREFIX instead of abusing $(INSTALL_ROOT).
Reason: $INSTALL_ROOT is only meant to be used by packagers to temporarily put the contents into a different location, which is needed for fakeroot packaging. QTC_PREFIX is not a qmake variable, and defaults to /usr/local. On Windows the default prefix is "QtCreator", since "make install" is expected to be used in a packaging context only where either INSTALL_ROOT should be used or QTC_PREFIX should be set to the absolute destination path where e.g. an installer generator will pick it up. Change-Id: Ifa4950340e58e34726c53f5417adcc7b50828ce1 Reviewed-by: Oswald Buddenhagen <firstname.lastname@example.org>