the new $RELOCATEABLE_OUTPUT_FORMAT, if set.
(OUTPUT_FORMAT): Use the variable $OUTPUT_FORMAT.
(ENTRY): Don't emit for relocateable links.
(/DISCARD/): Don't discard .gnu.warning.* for relocateable links.
* emulparams/mmo.sh (RELOCATEABLE_OUTPUT_FORMAT): Set, to
elf64-mmix.
* emulparams/elf64mmix.sh (OTHER_TEXT_SECTIONS): Empty, don't
provide "Main" or set "_start.", for relocateable links.