CMake 3.27 deprecates compatibility with CMake < 3.5.  Update tests that
do not cover older interfaces to avoid the deprecation warning.

Follow the pattern from:

* commit 7b07ccdd2b (Tests/*Only: Update cmake_minimum_required versions,
                     2020-06-15, v3.19.0-rc1~629^2~1)

* commit 72e7c45e98 (Tests: Bump CMake minimum required in tests to 2.8.12,
                     2020-12-22, v3.20.0-rc1~224^2)

* commit f6b4db365a (Tests: bump cmake_minimum_required version to 2.8.12,
                     2021-04-04, v3.21.0-rc1~372^2)

Also remove explicit `cmake_policy` settings made redundant by the
version.

Sources that use `atoi` need to include `<stdlib.h>`.

This needlessly produces warnings during the test runs that no-one
sees but that are distracting when actually inspecting the logs.

Run the `clang-format.bash` script to update all our C and C++ code to a
new style defined by `.clang-format`.  Use `clang-format` version 6.0.

* If you reached this commit for a line in `git blame`, re-run the blame
  operation starting at the parent of this commit to see older history
  for the content.

* See the parent commit for instructions to rebase a change across this
  style transition commit.

Some are user facing.

Found using

    codespell -q 3 --skip="./Utilities" -I .cmake-whitelist.txt`

whereby the whitelist contained:

    ans
    dum
    helpfull
    emmited
    emmitted
    buil
    iff
    isnt
    nto
    ot
    pathes
    substract
    te
    todays
    upto
    whitespaces

Fix tests to account for commit 243aed52 (cmTimestamp: Support
SOURCE_DATE_EPOCH to override current time, 2017-01-25).

In openSUSE we are running the test-suite as part of the build and that
failed in these two places when building everything with
`SOURCE_DATE_EPOCH` set.

This adds the LESS_EQUAL, GREATER_EQUAL, and associated STR and VERSION
equivalents to use the combined <= and >= functionality.