cmake: avoid GLOB for *.msg files and use an explicit .msg file enumeration

This makes sure that adding & removing of .msg files is handled properly
by the build system.

cmake/common/px4_base.cmake

@@ -415,6 +415,13 @@ function(px4_generate_messages)
 		)
 	set_source_files_properties(${msg_source_files_out} PROPERTIES GENERATED TRUE)
 
+	# We remove uORBTopics.cpp to make sure the generator is re-run, which is
+	# necessary when a .msg file is removed and because uORBTopics.cpp depends
+	# on all topics.
+	execute_process(COMMAND rm uORBTopics.cpp
+		WORKING_DIRECTORY ${msg_source_out_path}
+		ERROR_QUIET)
+
 	# multi messages for target OS
 	set(msg_multi_out_path
 		${CMAKE_BINARY_DIR}/src/platforms/${OS}/px4_messages)