Apparently, I do have UTF-16 available on this machine (Solaris 10 on x86).
As the attached C program shows, a call to iconv_open with identical "to" and
"from" arguments fails with errno 22 (meaning that the conversion is not
available).  But a conversion from "ISO8859-1" to "UTF-16" (or vice versa)
is valid (iconv_open returns a valid descriptor instead of -1).  So it appears
that the method of passing the same codeset as both "to" and "from" arguments
to determine if that codeset is present does not work on Solaris.

However, this same behavior occurs on Solaris SPARC, so now I don't understand
why Solaris SPARC external commands do not fail.