iconv without "wchar_t" as a conversion name

["Paul Koning" <Paul_Koning@Dell.com>]

NetBSD has iconv support, essentially the same as in glibc, with one
crucial difference that messes up GDB.

In gdb_wchar.h, INTERMEDIATE_ENCODING is hardcoded as "wchar_t" and in
charset.c iconv_open() is called with INTERMEDIATE_ENCODING as the "to"
format.

As it happens, the NetBSD implementation of iconf does not list
"wchar_t" as a format it knows, though it does have a very long list of
supported formats that looks otherwise quite similar to what iconv on,
say, Linux supports.

I assume "wchar_t" means "whatever character format is the native
encoding of a wchar_t data type".  If so, it looks like "ucs-4" would be
a valid replacement, since wchar_t maps to int on NetBSD.  This suggest
that INTERMEDIATE_ENCODING should be determined by configure instead of
being hardcoded.

Does this make sense?  I can work on a patch, though hints on how to do
this in configure would be welcome since I'm a beginner in that space.

	paul