ipc: Always build the ipc-struct.txt file in the build root

Part-of: <https://gitlab.freedesktop.org/monado/monado/-/merge_requests/2635>

src/xrt/ipc/CMakeLists.txt

···
 		)
 endforeach()
 
+# Generate IPC structures list in the build root
+add_custom_command(
+	OUTPUT "${CMAKE_BINARY_DIR}/ipc-structs.txt"
+	COMMAND
+		${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/shared/proto.py
+		${CMAKE_CURRENT_SOURCE_DIR}/shared/proto.json
+		"${CMAKE_BINARY_DIR}/ipc-structs.txt"
+	VERBATIM
+	DEPENDS
+		${CMAKE_CURRENT_SOURCE_DIR}/shared/proto.py
+		${CMAKE_CURRENT_SOURCE_DIR}/shared/ipcproto/common.py
+		${CMAKE_CURRENT_SOURCE_DIR}/shared/proto.json
+	COMMENT "Generating ipc-structs.txt from protocol JSON description"
+	)
+
+add_custom_target(ipc_structs_list ALL DEPENDS "${CMAKE_BINARY_DIR}/ipc-structs.txt")
+
 set(IPC_COMMON_SOURCES
     ${CMAKE_CURRENT_BINARY_DIR}/ipc_protocol_generated.h
     shared/ipc_message_channel.h

src/xrt/ipc/shared/proto.py

···
             generate_server_c(output, p)
         if output.endswith("ipc_server_generated.h"):
             generate_server_header(output, p)
-        if output.endswith("structs.txt"):
+        if output.endswith("structs.txt") or output.endswith("ipc-structs.txt"):
             generate_struct_names(output, p)