binutils: make it a proper package

* Convert binutils to a proper autotargets package

* Add version 2.21 and drop version 2.17

* Hook up packaged binutils for target gcc

* Build tools are on HOST_DIR now so change it

* Move cross/host gcc to HOST_DIR

* Drop kludge from commit 3c77bab2
  This is fixed in the next commit "gcc: install copies of libgcc,
  libstdc++ and libgcj to the sysroot" - tested for arm & x86_64
  targets.

* TARGET_CROSS now pointed to HOST_DIR too

[Peter: Config.in tweaks]
Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>