Fix build of mediastream tool on Linux with CMake.

tools/CMakeLists.txt

@@ -37,7 +37,11 @@ if (PCAP_FOUND)
 	target_link_libraries(pcap_playback ${PCAP_LIBRARIES})
 endif()
 
-add_executable(mediastream mediastream.c common.c mediastream_cocoa.m)
+set(MEDIASTREAM_SOURCE_FILES mediastream.c common.c)
+if(APPLE)
+	list(APPEND MEDIASTREAM_SOURCE_FILES mediastream_cocoa.m)
+endif()
+add_executable(mediastream ${MEDIASTREAM_SOURCE_FILES})
 target_link_libraries(mediastream mediastreamer_voip mediastreamer_base)
 string(REPLACE ";" " " APPLE_SPECIFIC_LINK_FLAGS_STR "${APPLE_SPECIFIC_LINK_FLAGS}")
 if(NOT "${APPLE_SPECIFIC_LINK_FLAGS_STR}" STREQUAL "")