Speedup mmo and pe orphan placement for relocatable link

Since there is no need to place output sections in specific order for
relocatable link, we can skip merging flags of other input sections.

	PR ld/19739
	* emultempl/mmo.em (mmo_place_orphan): Don't merge flags of other
	input sections for relocatable link.
	* emultempl/pe.em (gld_${EMULATION_NAME}_place_orphan): Likewise.
	* emultempl/pep.em (gld_${EMULATION_NAME}_place_orphan): Likewise.