add ext-toolchain.sh, a utility for external toolchains The ext-toolchain.sh utility script implements various external toolchain tasks: * Testing of available features, like c++, soft-float or ipv6 support * Finding the libc implementation (uclibc or eglibc/glibc) * Inferring the GNU target name * Finding shared objects for packaging (libc, libpthread, ...) * Finding executables for packaging (ldd, gdbserver, ...) * Generating wrapper scripts for toolchain commands

SVN-Revision: 29765