OK, I forgot that they use a weird target triplet.
Unapply (or revert) the previous patch, and try the attached patches.
Also, in addition to the packages listed for Debian in the Compatibility thread, I needed to install libx11-dev and libxext-dev. Though this wasn't from a clean install (just a Pi 3 I had around from some other previous use), so some other necessary things might have already been installed.
arm_gnueabihf_fix.txt will fix the qt auto-detection.
qmin_template_fix.txt will fix the compile error in bazaarlog.cpp
With those patches and the extra packages, it compiles on an older version of OSMC (based on Debian Stretch) on a Pi 3. If they work for you, I'll go ahead an apply them to the beta branch.