Pull up following revision(s) (requested by pgoyette in ticket #757):

sys/conf/files: revision 1.1257
sys/conf/files: revision 1.1258
sys/conf/files: revision 1.1259

mips64 has compat_netbsd32 but cannot have exec_aout; all other users
of compat_netbsd32 need exec_aout

Addresses PR kern/55037.
XXX pullup-9

Fix comment - thanks Ryo Shimizu

Also exclude EXEC_AOUT stuff for aarch64
XXX Pullup-9 and -8

(martin)