Add variant 'nls' for native language support with default True.
The default inside binutils was always on, but this gives a way of
turning it off, if desired.
Adjust the dependencies. Flex is never used for a one-time build.
Bison and m4 should not be needed, except that prior to rev 2.30, gold
did not include its generated files, so bison is needed when +gold.
Drop configure option --enable-interwork. This option does not exist.