debug/gdb: install ncurses in a temporary place

We only build the static ncurses, to be used to build the native gdb,
and it needs not be available for anyone but us. So install it into
a temporary place, and get rid of it once gdb is built.

# Compute IA-64-specific values

CT_DoArchTupleValues() {

    # The architecture part of the tuple:

    CT_TARGET_ARCH="${CT_ARCH}"

}