Added elf library for elf code. #1270

Job	Run time
build (nightly) / rust	28s
build (msrv) / rust	53s
build (stable) / rust	26s
build no_std (stable) [w/o builder] / rust	21s
style (stable) / rust	19s
build no_std (stable) [Windows] / rust	2m 7s
build no_std (stable) / rust	19s
style (nightly) / rust	21s
build no_std (nightly) / rust	23s
tests with miri (nightly) / rust	1m 21s
style (msrv) / rust	23s
build no_std (msrv) / rust	27s
	7m 48s

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