crosstool-ng: Pull in cross-gdb GCC library static linking support

This commit pulls in the GCC library (`libstdc++` and `libgcc`) static
linking support for the cross-gdb (`CT_GDB_CROSS_STATIC_LIBSTDCXX`).

Note that `CT_GDB_CROSS_STATIC_LIBSTDCXX` is enabled by default and no
changes are required on the Zephyr SDK side for this to take effect.

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: stephanosio