[Unsttopabull]

Summary

ubuntu-latest now runs on the ubuntu-26.04 image (GCC 15.2, glibc 2.43). There, the Linux build-and-test jobs fail while compiling the fetched paho.mqtt.c v1.3.15:

src/MQTTProtocolOut.c:64:19: error: assignment discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]

glibc 2.43 makes strrchr() return const char* when it is given a const char*. Paho assigns the result to a char*.

The warning becomes an error because the openDAQ cmake utils add -Werror to the whole directory with add_compile_options and the Paho targets inherit it.

On Windows we already build Paho with /WX- /W0. This PR gives GCC/Clang the same treatment.
No Paho release fixes this. The line is unchanged in v1.3.16 and on master.

Changes

• external/paho_mqtt_c/CMakeLists.txt: the per-target loop over the Paho targets now runs on every platform, not only on Windows. The WIN32_LEAN_AND_MEAN/winsock definitions remain Windows-only. MSVC keeps /WX- /W0, and other compilers get -Wno-error. The warning is still printed but no longer fails the build. Only the Paho targets are affected, so module code keeps -Werror.

Testing

• Ubuntu 26.04.1 container (GCC 15.2, glibc 2.43):
  • Paho v1.3.15 alone with the same directory-wide -Werror: fails on MQTTProtocolOut.c:64 without the change and builds with it.
  • Full module, Debug, with the CI configure line (-DDAQMODULES_MQTT_ENABLE_TESTS=ON -DDAQMODULES_MQTT_DEBUG_WARNINGS_AS_ERRORS=ON -DOPENDAQ_DEBUG_WARNINGS_AS_ERRORS=ON): builds, and MQTTProtocolOut.c now reports a warning instead of an error. test_mqtt_streaming_protocol and test_mqtt_stream_module pass with a local mosquitto.
• Windows, Visual Studio 18 2026 x64, Debug: builds. The Paho projects still get /WX-, warning level 0 and WIN32_LEAN_AND_MEAN.
• Release on Linux was not built locally. It takes the same -Werror path (Release warnings-as-errors is on by default).

[viacheslauK]

LGTM