fix(mosq): Fix clean compilation addressing _GNU_SOURCE redefined

Author: david-cermak

.github/workflows/mosq__build.yml

@@ -25,8 +25,6 @@ jobs:
         with:
           submodules: recursive
       - name: Build with IDF-${{ matrix.idf_ver }}
-        env:
-          EXPECTED_WARNING: "\"_GNU_SOURCE\" redefined"
         shell: bash
         run: |
           . ${IDF_PATH}/export.sh

components/mosquitto/CMakeLists.txt

@@ -82,3 +82,11 @@ idf_component_register(SRCS ${m_srcs}
 
 target_compile_definitions(${COMPONENT_LIB} PRIVATE "WITH_BROKER")
 target_compile_options(${COMPONENT_LIB} PRIVATE "-Wno-format")
+
+# Some mosquittos source unconditionally define `_GNU_SOURCE` which collides with IDF build system
+# producing warning: "_GNU_SOURCE" redefined
+# This workarounds this issue by undefining the macro for the selected files
+set(sources_that_define_gnu_source ${m_lib_dir}/net_mosq.c ${m_src_dir}/loop.c ${m_src_dir}/mux_poll.c)
+foreach(offending_src ${sources_that_define_gnu_source})
+    set_source_files_properties(${offending_src} PROPERTIES COMPILE_OPTIONS "-U_GNU_SOURCE")
+endforeach()