Instead of hardcoding a list of platforms where libedit is known to have
wide char support we detect this in cmake. The main motivation for this
is attempting to improve compatibility with different versions of
libedit, as the interface of non-wide-char functions varies slightly
This should be NFC on all platforms except linux. On linux, we used to
hardcode to non-wide-char, now we will use wide-char if we detect
libedit supports that.