Fix port to glibc 2.24 (pre-release) + ppc64

Fix port to glibc 2.24 (pre-release) + ppc64

* src/callproc.c (child_setup): Use emacs_exec_file
so that ASLR is enabled in the child process.
* src/emacs.c: Move some personality details into sys/sysdep.c.
Do not include <sys/personality.h>.
(main): Disable ASLR earlier, so that we don’t chdir twice.
* src/lisp.h (disable_address_randomization): New decl.
* src/sysdep.c (disable_address_randomization)
[HAVE_PERSONALITY_ADDR_NO_RANDOMIZE]: Move personality details
here from emacs.c.
(emacs_exec_file): New function.