[solaris] fix -Werror=implicit-function-declaration on getopt()

Author: Matthieu Longo

proton-c/CMakeLists.txt

@@ -251,6 +251,10 @@ if (CMAKE_COMPILER_IS_GNUCC)
     set (COMPILE_WARNING_FLAGS "${CXX_WARNING_FLAGS}")
   endif (NOT BUILD_WITH_CXX)
 
+  if (CMAKE_HOST_SOLARIS)
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -D__EXTENSIONS__")
+  endif (CMAKE_HOST_SOLARIS)
+
   if (ENABLE_UNDEFINED_ERROR)
     if (CMAKE_HOST_SOLARIS)
       set (CATCH_UNDEFINED "-zdefs")
@@ -292,6 +296,7 @@ set(CXX_WARNING_FLAGS "${CXX_WARNING_FLAGS}" PARENT_SCOPE)
 set(COMPILE_WARNING_FLAGS "${COMPILE_WARNING_FLAGS}" PARENT_SCOPE)
 set(COMPILE_LANGUAGE_FLAGS "${COMPILE_LANGUAGE_FLAGS}" PARENT_SCOPE)
 set(LINK_TIME_OPTIMIZATION "${LTO}" PARENT_SCOPE)
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS}" PARENT_SCOPE)
 
 if (MSVC)
     set(CMAKE_DEBUG_POSTFIX "d")