This is a followup to bf182596a9d85604f6f029302671a38001575355.
* gnu/packages/games.scm (prboom-plus, red-eclipse, btanks)
(edgar): Use 'search-input-directory' instead of 'search-input-file'
when looking for "include/SDL".
(abbaye): Likewise, and search "include/SDL2" instead of "include/SDL".