* sysdeps/unix/sysv/linux/dl-execstack.c (_dl_make_stack_executable):
Don't check for zero __libc_stack_end, it should be initialized.
[_STACK_GROWS_DOWN] [PROT_GROWSDOWN]: Try using PROT_GROWSDOWN flag
and fall back if it fails with EINVAL.
[_STACK_GROWS_UP] [PROT_GROWSUP]: Likewise for PROT_GROWSUP.