Avoid a const cast warning

This is in very old iconv code, probably before compilers got serious,
or people did, about making sure const was... well obeyed.
Output is iconv, not libiconv!

Was causing all the make files to "fail". :(
Cascade the targets in cmake

iconv wasn't being built for glib because we were doing dependencies in
a funny way. This normalizes the dependencies by explicit targets, which
makes things much nicer.
Build properly for external linkages

Was missing GLIB_COMPILATION, and a few others things pulled from the
true make file for this guy.
Get rid of compilation warnings in glib

minor things, shouldn't change the meaning (I hope!).
Supress unused variable warnings in gdk build

Make sure it looks good!