Can you check CMakeFiles/CMakeError.log and the other log files for Mord information?
Sure. There's nothing in CMakeError that has anything to do with readline.
[solskogen@centos-rpi hatari-build]$ grep -ri readli .
./config.h:/* Define if you have a readline compatible library */
./config.h:/* #undef HAVE_LIBREADLINE */
./CMakeFiles/Makefile.cmake: "/home/solskogen/hatari/cmake/FindReadline.cmake"
./src/CMakeFiles/hatari.dir/build.make:src/hatari: /usr/lib/libreadline.so
./src/CMakeFiles/hatari.dir/link.txt:/usr/bin/cc -std=gnu99 -Wcast-qual -Wbad-function-cast -Wpointer-arith -Wmissing-prototypes -Wstrict-prototypes -Wall -Wwrite-strings -Wsign-compare -Wformat-security -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -O3 -DNDEBUG CMakeFiles/hatari.dir/acia.c.o CMakeFiles/hatari.dir/audio.c.o CMakeFiles/hatari.dir/avi_record.c.o CMakeFiles/hatari.dir/bios.c.o CMakeFiles/hatari.dir/blitter.c.o CMakeFiles/hatari.dir/cart.c.o CMakeFiles/hatari.dir/cfgopts.c.o CMakeFiles/hatari.dir/clocks_timings.c.o CMakeFiles/hatari.dir/configuration.c..o CMakeFiles/hatari.dir/options.c.o CMakeFiles/hatari.dir/change.c.o CMakeFiles/hatari.dir/control.c.o CMakeFiles/hatari.dir/cycInt.c.o CMakeFiles/hatari.dir/cycles.c.o CMakeFiles/hatari.dir/dialog.c.o CMakeFiles/hatari.dir/dmaSnd.c.o CMakeFiles/hatari.dir/fdc.c.o CMakeFiles/hatari.dir/file.c.o CMakeFiles/hatari.dir/floppy.c.o CMakeFiles/hatari.dir/floppy_ipf.c.o CMakeFiles/hatari.dir/floppy_stx.c.o CMakeFiles/hatari.dir/gemdos.c.o CMakeFiles/hatari.dir/hd6301_cpu.c.o CMakeFiles/hatari.dir/hdc.c.o CMakeFiles/hatari.dir/ide.c.o CMakeFiles/hatari.dir/ikbd.c.o CMakeFiles/hatari.dir/ioMem.c.o CMakeFiles/hatari.dir/ioMemTabST.c.o CMakeFiles/hatari.dir/ioMemTabSTE.c.o CMakeFiles/hatari.dir/ioMemTabTT.c.o CMakeFiles/hatari.dir/ioMemTabFalcon.c.o CMakeFiles/hatari.dir/joy.c.o CMakeFiles/hatari.dir/keymap.c.o CMakeFiles/hatari.dir/m68000.c.o CMakeFiles/hatari.dir/main.c.o CMakeFiles/hatari.dir/midi.c.o CMakeFiles/hatari.dir/memorySnapShot.c.o CMakeFiles/hatari.dir/mfp.c.o CMakeFiles/hatari.dir/nf_scsidrv.c.o CMakeFiles/hatari.dir/ncr5380.c.o CMakeFiles/hatari.dir/paths.c.o CMakeFiles/hatari.dir/psg.c.o CMakeFiles/hatari.dir/printer.c.o CMakeFiles/hatari.dir/resolution.c.o CMakeFiles/hatari..dir/rs232.c.o CMakeFiles/hatari.dir/reset.c.o CMakeFiles/hatari.dir/rtc.c.o CMakeFiles/hatari.dir/scandir.c.o CMakeFiles/hatari.dir/scc.c.o CMakeFiles/hatari.dir/stMemory.c.o CMakeFiles/hatari.dir/screen.c.o CMakeFiles/hatari.dir/screenConvert.c.o CMakeFiles/hatari.dir/screenSnapShot.c.o CMakeFiles/hatari.dir/shortcut.c.o CMakeFiles/hatari.dir/sound.c.o CMakeFiles/hatari.dir/spec512.c.o CMakeFiles/hatari.dir/statusbar.c.o CMakeFiles/hatari.dir/str.c.o CMakeFiles/hatari.dir/tos.c.o CMakeFiles/hatari.dir/utils.c.o CMakeFiles/hatari.dir/vdi.c.o CMakeFiles/hatari.dir/inffile.c.o CMakeFiles/hatari..dir/video.c.o CMakeFiles/hatari.dir/wavFormat.c.o CMakeFiles/hatari.dir/xbios.c.o CMakeFiles/hatari.dir/ymFormat.c.o CMakeFiles/hatari.dir/lilo.c.o CMakeFiles/hatari.dir/unzip.c.o -o hatari -L/home/solskogen/hatari-build/src/debug -L/home/solskogen/hatari-build/src/falcon -L/home/solskogen/hatari-build/src/gui-sdl -L/home/solskogen/hatari-build/src/cpu -rdynamic falcon/libFalcon.a cpu/libUaeCpu.a gui-sdl/libGuiSdl.a libFloppy.a debug/libDebug.a -lSDL2 -lpthread -lm -lreadline -lz -lpng -lX11 -lXext -lportaudio -Wl,-rpath,/home/solskogen/hatari-build/src/debug:/home/solskogen/hatari-build/src/falcon:/home/solskogen/hatari-build/src/gui-sdl:/home/solskogen/hatari-build/src/cpu:
./src/debug/CMakeFiles/Debug.dir/flags.make:C_FLAGS = -std=gnu99 -Wcast-qual -Wbad-function-cast -Wpointer-arith -Wmissing-prototypes -Wstrict-prototypes -Wall -Wwrite-strings -Wsign-compare -Wformat-security -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -O3 -DNDEBUG -I/home/solskogen/hatari/src/includes -I/home/solskogen/hatari/src/debug -I/home/solskogen/hatari/src/falcon -I/home/solskogen/hatari-build -I/usr/include/SDL2 -I/home/solskogen/hatari/src/cpu -I/usr/include/readline -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64
./src/debug/CMakeFiles/Debug.dir/DependInfo.cmake: "/usr/include/readline"
./CMakeCache.txt:READLINE_INCLUDE_DIR:PATH=/usr/include/readline
./CMakeCache.txt:READLINE_LIBRARY:FILEPATH=/usr/lib/libreadline.so
./CMakeCache.txt://Details about finding Readline
./CMakeCache..txt:FIND_PACKAGE_MESSAGE_DETAILS_Readline:INTERNAL=[/usr/lib/libreadline..so][/usr/include/readline][v()]
./CMakeCache.txt://ADVANCED property for variable: READLINE_INCLUDE_DIR
./CMakeCache.txt:READLINE_INCLUDE_DIR-ADVANCED:INTERNAL=1
./CMakeCache.txt://ADVANCED property for variable: READLINE_LIBRARY
./CMakeCache.txt:READLINE_LIBRARY-ADVANCED:INTERNAL=1
And this is the files in /usr/include/readline:
[solskogen@centos-rpi hatari-build]$ ls -l /usr/include/readline/
total 76
-rw-r--r--. 1 root root 4578 Aug 8 2019 chardefs.h
-rw-r--r--. 1 root root 10078 Aug 8 2019 history.h
-rw-r--r--. 1 root root 3163 Aug 8 2019 keymaps.h
-rw-r--r--. 1 root root 36644 Aug 8 2019 readline.h
-rw-r--r--. 1 root root 2189 Aug 8 2019 rlconf.h
-rw-r--r--. 1 root root 1546 Aug 8 2019 rlstdc.h
-rw-r--r--. 1 root root 2845 Aug 8 2019 rltypedefs.h
-rw-r--r--. 1 root root 3046 Aug 8 2019 tilde.h