Get rid of lsb-build multiarch build hack

[davidben]

Or at least make the lsb-build thing coherent. I think we're missing X11 headers right now.

Unfortunately, Linux does not appear to have a coherent way to correctly cross-compile things with system libraries. Existing patches just assume that the host architecture pkg-config flags and headers will work which is not necessarily true. Instead, we should require, say, pkg-config files for the viewer architecture and pass that along a command-line flag to configure until distributions can stop disagreeing on where the files live.

It would also be nice to switch to a better buildsystem or allow building multiple architectures' worth of viewers.

(In fact, reusing CFLAGS already doesn't work for glib. glibconfig.h is architecture-specific. lsb-build gets around this by defining all the macros with piles of architecture ifdefs.)