GH-50487: [C++] Extra semicolon warning from ARROW_SUPPRESS_DEPRECATION_WARNING macro with -Wpedantic

[thisisnic]

Rationale for this change

The ARROW_SUPPRESS_DEPRECATION_WARNING and ARROW_SUPPRESS_MISSING_DECLARATIONS_WARNING macros have trailing semicolons after _Pragma directives, which produce empty statements and trigger -Wpedantic warnings wherever the macros are used.

What changes are included in this PR?

Remove unnecessary semicolons after _Pragma calls in the clang, GCC, and missing-declarations macro variants in macros.h.

Are these changes tested?

Existing tests cover these macros. The change only removes empty statements.

Are there any user-facing changes?

No.

• GitHub Issue: [C++] Extra semicolon warning from ARROW_SUPPRESS_DEPRECATION_WARNING macro with -Wpedantic #50487

[github-actions]

⚠️ GitHub issue #50487 has been automatically assigned in GitHub to PR creator.

[Copilot]

Pull request overview

This PR fixes -Wpedantic warnings caused by empty statements emitted from warning-suppression macros in Arrow C++ headers. It updates cpp/src/arrow/util/macros.h so _Pragma(...) uses no trailing semicolons, preventing “extra ‘;’” warnings at macro expansion sites.

Changes:

• Remove trailing semicolons after _Pragma(...) in the Clang and GCC ARROW_SUPPRESS_DEPRECATION_WARNING macro variants.
• Remove trailing semicolons after _Pragma(...) in ARROW_SUPPRESS_MISSING_DECLARATIONS_WARNING for GCC.