Adjust iteration counts so benchmarks don't run too slowly or quickly.
Ensure benchmarks take less than 10 seconds on older, slower cores and
more than 0.5 seconds on fast cores.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

Instead of benchmarking slow byte oriented loops, include the optimized
generic memchr/memrchr implementation.  Adjust iteration count to reduce
benchmark time.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

1. Add more complete coverage in the medium size range.
2. In strnlen remove the `1 << i` which was UB (`i` could go beyond
   32/64)

Add a second iteration for memrchr to set `pos` starting from the end
of the buffer.

Previously `pos` was only set relative to the beginning of the
buffer. This isn't really useful for memrchr because the beginning
of the search space is (buf + len).
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

1. Use json_ctx for output to help standardize format across all
   benchtests.

2. Add some additional tests to strstr and memchr expanding alignments
   and adding more small values.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

I used these shell commands:

../glibc/scripts/update-copyrights $PWD/../gnulib/build-aux/update-copyright
(cd ../glibc && git commit -am"[this commit message]")

and then ignored the output, which consisted lines saying "FOO: warning:
copyright statement not found" for each of 7061 files FOO.

I then removed trailing white space from math/tgmath.h,
support/tst-support-open-dev-null-range.c, and
sysdeps/x86_64/multiarch/strlen-vec.S, to work around the following
obscure pre-commit check failure diagnostics from Savannah.  I don't
know why I run into these diagnostics whereas others evidently do not.

remote: *** 912-#endif
remote: *** 913:
remote: *** 914-
remote: *** error: lines with trailing whitespace found
...
remote: *** error: sysdeps/unix/sysv/linux/statx_cp.c: trailing lines

No bug. This commit adds some additional cases for bench-memchr.c
including testing medium sizes and testing short length with both an
inbound match and out of bound match.

Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>