Use auxiliary vector to obtain the executable path name (#24696)

Use auxiliary vector to obtain the executable path name (#24696)

This vector is populated by the kernel while loading an ELF, and is
available to user land without requiring any system calls.  This is
specially interesting if programs are executed under a chroot where
/proc isn't available (and thus realpath("/proc/self/exe"), the current
method of obtaining the full path name for the executable).