25d37948c9 ("malloc: Improve malloc initialization") moved calling malloc
initialization earlier, within _dl_sysdep_start's call to dl_main, before
__mach_init is called by _dl_init_first. But malloc initialization uses
getrandom, which needs to make RPCs.
This adds __getrandom_early_init on hurd to express that getrandom needs
__mach_init too. This also adds a guard to avoid making it create several task
and host ports.
Fixes: 25d37948c9 ("malloc: Improve malloc initialization")
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>