C90 compatible headers

[justsmth]

Issues:

Resolves #ISSUE-NUMBER1
Addresses #ISSUE-NUMBER2

Description of changes:

Describe AWS-LC’s current behavior and how your code changes that behavior. If there are no issues this pr is resolving, explain why this change is necessary.

Call-outs:

Point out areas that need special attention or support during the review process. Discuss architecture or design changes.

Testing:

How is this change tested (unit tests, fuzz tests, etc.)? Are there any testing steps to be verified by the reviewer?

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 ✅

Project coverage is 79.03%. Comparing base (acdf53b) to head (1686fca).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2213      +/-   ##
==========================================
- Coverage   79.04%   79.03%   -0.01%     
==========================================
  Files         612      612              
  Lines      106239   106238       -1     
  Branches    15009    15009              
==========================================
- Hits        83980    83970      -10     
- Misses      21607    21616       +9     
  Partials      652      652              

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