benchtests: Make memcpy benchmarks print results in json

benchtests: Make memcpy benchmarks print results in json

Print the benchmark output for various memcpy benchmarks in json so
that it can be predictably parsed and analyzed.

	* benchtests/bench-memcpy-large.c: Include json-lib.h.
	(do_one_test): Print json.
	(do_test): Likewise.
	(test_main): Likewise.
	* benchtests/bench-memcpy-random.c: Include json-lib.h.
	(do_one_test): Print json.
	(do_test): Likewise.
	(test_main): Likewise.
	* benchtests/bench-memcpy.c: Include json-lib.h.
	(do_one_test): Print json.
	(do_test): Likewise.
	(test_main): Likewise.