buildtools-extended-tarball: Add glibc-gconvs needed for build
When building vim it tries to rebuild files using iconv. If this fails
the build continues anyway but the output is not determnistic as builds
using a hosttools tarball are different from builds where there isn't a
hosttools tarball. Add the needed gconvs to the tarball when iconv is
present to become determistic and generate vim locales consistently.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
