Belatedly update Doom Legacy to version 1.47.2 (r1412) and unbreak.

The new features include MBF (Marine's Best Friend) compatibility, support
for sprites with 16 rotation positions, the possibility of multiple clients
and the server running on the same computer, plus many bug fixes.

While here, move ${DMDIR} up in WAD search list (DEFWADS20 -> DEFWADS04),
add ASM_BROKEN and missing `gl' to USE_GL, improve diagnostics and fix
potential segmentation fault in the owner_wad_search_order() function.