Ports that provide DOOM data files (WADs), like games/doomdata (with
shareware game data) and games/freedoom (with free game data), install
them at /usr/local/share/doom/.

Ports for other DOOM engines, like games/crispy-doom, also expect WADs
to be there.

Index: prboom2/CMakeLists.txt
--- prboom2/CMakeLists.txt.orig
+++ prboom2/CMakeLists.txt
@@ -167,7 +167,7 @@ endif()
 if(WIN32)
     set(DEFAULT_WAD_DIR ".")
 else()
-    set(DEFAULT_WAD_DIR "share/games/doom")
+    set(DEFAULT_WAD_DIR "share/doom")
 endif()
 
 set(DSDAPWADDIR "${DEFAULT_WAD_DIR}" CACHE STRING "Path to install DSDA-Doom internal WAD, relative to CMAKE_INSTALL_PREFIX or absolute.")
