fix -Wmissing-prototypes for neon extension

[skyzh]

Problem

ref #6188

Summary of changes

This pull request fixes -Wmissing-prototypes for the neon extension. Note that (1) the gcc version in CI and macOS is different, therefore some of the warning does not get reported when developing the neon extension locally. (2) the CI env variable COPT = -Werror does not get passed into the docker build process, therefore warnings are not treated as errors on CI.

neon/.github/workflows/build_and_test.yml

Line 22 in e62baa9

COPT: '-Werror'

There will be follow-up pull requests on solving other warnings. By the way, I did not figure out the default compile parameters in the CI env, and therefore this pull request is tested by manually adding -Wmissing-prototypes into the COPT.

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[save-buffer]

Thanks for doing this!

[github-actions]

2484 tests run: 2361 passed, 0 failed, 123 skipped (full report)

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Flaky tests (5)

Postgres 16

• test_timeline_deletion_with_files_stuck_in_upload_queue: release
• test_empty_branch_remote_storage_upload: debug

Postgres 15

• test_tenant_delete_smoke: release

Postgres 14

• test_wal_restore: release
• test_wal_restore_initdb: release

Code coverage* (full report)

• functions: 28.7% (6932 of 24172 functions)
• lines: 47.2% (42514 of 90097 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
ce91539 at 2024-03-04T20:54:18.531Z :recycle:}

[skyzh]

Hold this pull request until storage/compute release to avoid problems with changing C code unfamiliar to me (though I feel this modification is likely to be safe...). Will be included in next week's release.