rtld: Revert "When loading dso without PT_GNU_STACK phdr, only call"

After the removal of ia64 and sparc64, all current architectures
support executable stacks at an architectural level.

This reverts commit 1290d38ac50b3afa7e5781d9d97346a1042c736c.

Reviewed by: kib
Sponsored by: DARPA
Differential Revision: https://reviews.freebsd.org/D37904