gcc didn't like a couple of the changes (rightly so: one was actually
incorrect), and the fix for qfcc I didn't think to suggest while working
with Emily.
The general CFLAGS etc fixes mostly required just getting the order of
operations right: check for attributes after setting the warnings flags,
though those needed some care for gcc as it began warning about main
wanting the const attribute.
Fixing the imui link errors required moving the ui functions and setup
to vulkan_lighting.c, which is really the only place they're used.
