libc: string.h: add cmp functions tests

[maska989]

Description

Added

• memcmp(),
• strcmp(),
• strncmp(),
• strcoll()

function tests.

Motivation and Context

JIRA: CI-231

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

How Has This Been Tested?

• Already covered by automatic testing.
• New test added: (add PR link here).
• Tested by hand on: (list targets here).

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing linter checks and tests passed.
• My changes generate no new compilation warnings for any of the targets.

Special treatment

• This PR needs additional PRs to work (list the PRs, preferably in merge-order).
• I will merge this PR by myself when appropriate.

[damianloew]

Thanks for correcting the test to this version, it looks clear, but let's improve it a little bit.

[damianloew]

It was not applied, I've suggested sth similar, but with the ascii data and with checking two sizes in one iteration.

[damianloew]

Please also add a cases offsets to the rest of tested functions. I know it wasn't planned initially, but I think it will be worth as the implementation of strcmp for example is very close to the memcmp one. You would have to replace all of zeros with 1 for example when preparing test data for those functions and set NUL term (the rest of functions test strings).

[damianloew]

Small thing, but I think we should be consistent and start with a lowercase letter after suffix in commit message, so testdata: extend description for createCharStr

[damianloew]

LGTM, Let's wait with merge for #230