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.

 --- binutils/ld/ldmain.c

 +++ binutils/ld/ldmain.c

 @@ -293,2 +293,3 @@ main (int argc, char **argv)

    link_info.combreloc = TRUE;

 +  link_info.relro = TRUE;

    link_info.strip_discarded = TRUE;