x86_64: cmake: add rules to start the kernel under magenta_debug debugging

arch/x86_64/QEMU.cmake

@@ -6,6 +6,9 @@ endif ()
 
 find_program(LLDB lldb)
 find_program(GDB gdb)
+find_program(MXDBG
+	NAMES mxdbg
+	HINTS ${BUILD_TOOLS_DIR})
 
 set(patched_kernel ${CMAKE_CURRENT_BINARY_DIR}/kernel/${kernel_name}.elf32)
 set(generic_flags -m 128M -cpu qemu64,+rdrand)
@@ -63,6 +66,23 @@ if (image_cdrom)
 		DEPENDS ${image_cdrom})
 endif ()
 
+if (MXDBG)
+	message(STATUS "QEMU: Enable debugging with MXDBG")
+	add_custom_target(debug-kernel-mxdbg
+		COMMAND
+			nohup ${QEMU}
+				-kernel ${patched_kernel}
+				-initrd ${sys_dir}/${bsp_name}
+				--append kernel.enable-debugger
+				-serial tcp::7720,server,nowait & disown
+		COMMAND	sleep 0.5
+				&& ${MXDBG}
+					-r 127.0.0.1 7720
+				&& killall qemu-system-${TARGET_ARCH}
+		USES_TERMINAL
+		DEPENDS ${patched_kernel} bsp)
+endif ()
+
 if (LLDB)
 	message(STATUS "QEMU: Enable direct-kernel debug with LLDB")
 	add_custom_target(debug-kernel
@@ -71,6 +91,8 @@ if (LLDB)
 				-kernel ${patched_kernel}
 				-initrd ${sys_dir}/${bsp_name}
 				${generic_flags}
+				--append kernel.enable-debugger
+				-serial tcp::7720,server,nowait
 				-s -S &
 			${LLDB}
 				-o "file ${CMAKE_BINARY_DIR}/kernel/${kernel_name}.debug"