gcc: install copies of libgcc, libstdc++ and libgcj to the sysroot

We want to keep a copy around for the future SDK functionality.

Also it's a better fix for bug #1051.

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