cmake HAVE_LIB_FTS examples

nih-at/libzip CMakeLists.txt :150 

check_library_exists(fts fts_open "" HAVE_LIB_FTS)

flyinghead/flycast core/deps/libzip/CMakeLists.txt :138 

check_library_exists(fts fts_open "" HAVE_LIB_FTS)