Fix for C99; Add tests

[justsmth]

Issue

On macos, the collect_build_src.sh was not identifying refcount_lock.c as a source file b/c our automation performs the final build using the (default) C11 standard. However, refcount_lock.c is still needed for C99 builds, but it was not listed.

Description of changes:

• Updated collect_build_src.sh so that it will always include both refcount_lock.c and refcount_c11.c (although only one of these will actually be useful to any specific build).
• Added CI testing for popular platforms to verify that setting AWS_LC_SYS_C_STD to either 99 or 11 results in a successful build.
• Update the cc_builder source listing so that refcount_lock.c is included.

Testing:

• I ran the automated workflow and verified that the cc_builder source listings it produces match what's in this PR: https://github.com/aws/aws-lc-rs/actions/runs/10700676326
  • You can see the diff here: https://github.com/justsmth/aws-lc-rs/compare/testing-c-std...aws:aws-lc-rs:generate/aws-lc-sys-c99

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.52%. Comparing base (c358484) to head (9255fe2). Report is 78 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #513 +/- ## ========================================== - Coverage 95.80% 92.52% -3.28% ========================================== Files 61 67 +6 Lines 8143 9277 +1134 Branches 0 9277 +9277 ========================================== + Hits 7801 8584 +783 - Misses 342 422 +80 - Partials 0 271 +271 ```

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