[darobs]

Changes

Enable compiler diagnostics for ordinary builds. Currently, OpenTelemetry explicitly configures warning settings only when OTELCPP_MAINTAINER_MODE is enabled.

This change establishes a baseline warning policy for normal builds:  /W3 for MSVC and -Wall for GCC, Clang, and AppleClang. It does not introduce warnings-as-errors or additional warning suppressions.

Passing maintainer-mode CI does not ensure that SDK binaries produced by downstream applications or package managers were compiled with meaningful warnings enabled. This affects binary build-policy verification: Microsoft’s open-source BinSkim checks MSVC warning levels, while annocheck in the Red Hat/Fedora ecosystem checks whether warnings such as  -Wall were enabled.

For MSVC, this restores explicit baseline diagnostics following the removal of the CMP0092 compatibility workaround, without reinstating a deprecated CMake policy.

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.62%. Comparing base (0a5bb0b) to head (197f855).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4760   +/-   ##
=======================================
  Coverage   86.62%   86.62%           
=======================================
  Files         530      530           
  Lines       21169    21169           
=======================================
  Hits        18335    18335           
  Misses       2834     2834           

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