Add libiconv variant to glib (#10165)
Add libiconv variant to glib (#10165)

Enable explicitly building glib with or without libiconv.

Heads up: if you build with ~iconv but there is something else in the
spec that includes libiconv then glib will *still* automagically
discover it and the build will fail.
iulian787/spack,LLNL/spack,LLNL/spack,iulian787/spack,LLNL/spack,iulian787/spack,LLNL/spack,LLNL/spack,iulian787/spack,iulian787/spack