toolchain: add new debugging tool using magenta_debug

toolchain/mxdbg/server/CMakeLists.txt

@@ -0,0 +1,4 @@
+file(GLOB sources *.c *.h)
+
+add_executable(mxdbg-server ${sources})
+target_link_libraries(mxdbg-server magenta_debug)

toolchain/mxdbg/server/main.c

@@ -0,0 +1,4 @@
+int main(int argc, const char **argv)
+{
+	return 0;
+}