Prevent unnecessary multiple .el hashing in 'maybe_swap_for_eln'

Prevent unnecessary multiple .el hashing in 'maybe_swap_for_eln'

	* src/comp.c (Fcomp_el_to_eln_rel_filename): New function.
	(Fcomp_el_to_eln_filename): Make use of.
	(syms_of_comp): Register 'Scomp_el_to_eln_rel_filename'.
	* src/lread.c (maybe_swap_for_eln): Make use of
	'Fcomp_el_to_eln_rel_filename' to hash prevent unnecessary
	multiple hashing.