Bump up the runtime for "short" benchmarks

Some benchmarks with a very short runtime show significantly
different results across runs on Aarch64 - up to tens of percents.
Increasing the runtime to 100ms+ makes the deviation under 5%.

Tested on Aarch64 and x86-64.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

	* benchtests/bench-memccpy.c: Replace INNER_LOOP_ITERS
	with INNER_LOOP_ITERS_LARGE.
	* benchtests/bench-memchr.c: Likewise.
	* benchtests/bench-rawmemchr.c: Likewise.
	* benchtests/bench-strcat.c: Likewise.
	* benchtests/bench-strchr.c: Likewise.
	* benchtests/bench-string.h: Likewise.
	* benchtests/bench-strlen.c: Likewise.
	* benchtests/bench-strncpy.c: Likewise.
	* benchtests/bench-strnlen.c: Likewise.