build.rs: don't use `-pedantic` flag

[tmfink]

In some build systems, target sysroots may use non-standard C extentions like #include_next. In such cases, the -pedantic flag breaks the compilation.

Resolves issue #1923.

[tmfink]

Looks like there's an issue with the codecov CI job:

[2024-01-18T16:51:23.947Z] ['info'] Pinging Codecov: https://codecov.io/upload/v4?package=github-action-3.1.1-uploader-0.7.1&token=*******&branch=no-pedantic&build=7562601572&build_url=https%3A%2F%2Fgithub.com%2Fbriansmith%2Fring%2Factions%2Fruns%2F7562601572&commit=a4c3c83b91b34b2f0a8490579121b6e020f60bbe&job=ci&pr=1926&service=github-actions&slug=briansmith%2Fring&name=&tag=&flags=&parent=
[2024-01-18T16:51:23.947Z] ['verbose'] Passed token was 0 characters long
[2024-01-18T16:51:23.947Z] ['verbose'] https://codecov.io/upload/v4?package=github-action-3.1.1-uploader-0.7.1&branch=no-pedantic&build=7562601572&build_url=https%3A%2F%2Fgithub.com%2Fbriansmith%2Fring%2Factions%2Fruns%2F7562601572&commit=a4c3c83b91b34b2f0a8490579121b6e020f60bbe&job=ci&pr=1926&service=github-actions&slug=briansmith%2Fring&name=&tag=&flags=&parent=
        Content-Type: 'text/plain'
        Content-Encoding: 'gzip'
        X-Reduced-Redundancy: 'false'
[2024-01-18T16:51:24.173Z] ['error'] There was an error running the uploader: Error uploading to [https://codecov.io:](https://codecov.io/) Error: There was an error fetching the storage URL during POST: 404 - {'detail': ErrorDetail(string='Unable to locate build via Github Actions API. Please upload with the Codecov repository upload token to resolve issue.', code='not_found')}

https://github.com/briansmith/ring/actions/runs/7562601572/job/20625005568?pr=1926

[codecov[bot]]

Codecov Report

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

Comparison is base (73fb637) 91.58% compared to head (a4c3c83) 96.02%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1926 +/- ## ========================================== + Coverage 91.58% 96.02% +4.44% ========================================== Files 134 136 +2 Lines 19684 20776 +1092 Branches 226 226 ========================================== + Hits 18027 19950 +1923 + Misses 1623 792 -831 Partials 34 34 ```

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[briansmith]

Thank you! Merged.