global scope, wait for all lookups to finish afterwards.
* elf/dl-open.c (add_to_global): When global scope array must
grow, allocate a new one and free old array only after all
lookups finish.
* elf/dl-runtime.c (_dl_fixup): Protect using global scope.
(_dl_lookup_symbol_x): Likewise.
* elf/dl-support.c: Define _dl_wait_lookup_done.
* sysdeps/generic/ldsodefs.h (struct rtld_global): Add
_dl_wait_lookup_done.