How to tell whether mysql was built with libedit or readline?
If on Linux you can just use ldd to check which libraries it's dynamically linked against:

phil@ironforge:~$  ldd `which mysql`
        linux-vdso.so.1 =&gt;  (0x00007ffd5add5000)
        libpthread.so.0 =&gt; /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007eff0a44e000)
        libreadline.so.5 =&gt; /lib/x86_64-linux-gnu/libreadline.so.5 (0x00007eff0a210000)
        libncurses.so.5 =&gt; /lib/x86_64-linux-gnu/libncurses.so.5 (0x00007eff09fee000)
        libtinfo.so.5 =&gt; /lib/x86_64-linux-gnu/libtinfo.so.5 (0x00007eff09dc4000)
        libz.so.1 =&gt; /lib/x86_64-linux-gnu/libz.so.1 (0x00007eff09baa000)
        libdl.so.2 =&gt; /lib/x86_64-linux-gnu/libdl.so.2 (0x00007eff099a6000)
        libstdc++.so.6 =&gt; /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007eff09623000)
        libm.so.6 =&gt; /lib/x86_64-linux-gnu/libm.so.6 (0x00007eff0931a000)
        libc.so.6 =&gt; /lib/x86_64-linux-gnu/libc.so.6 (0x00007eff08f50000)
        /lib64/ld-linux-x86-64.so.2 (0x000055960d9f2000)
        libgcc_s.so.1 =&gt; /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007eff08d39000)
phil@ironforge:~$


In this example on my host, it's linked against libreadline.

It's also in the --help output:

phil@ironforge:~$ mysql --help | grep readline
mysql  Ver 15.1 Distrib 10.0.36-MariaDB, for debian-linux-gnu (x86_64) using readline 5.2
phil@ironforge:~$