Somewhere else in your makefile you'll have a target that depends on $(compiled_objs)
:
all_objects: $(compiled_objs)
Make will build the prerequisites of any target in the order they are listed. So if you want a particular object to be built last, then you just put it at the end of the compiled_objs
macro.
Be aware that during parallel builds make will still walk the commands to run in the same order, BUT due to parallelization effects they may actually run in a different order, or at least you can't know that the last one will be started after all the previous ones have completed.
For your situation I really don't recommend just stucking the last object at the end and hoping. You should define this relationship explicitly using make rules, so:
all_objects: xxxLast.o
xxxLast.o: $(compiled_objs-but-not-xxxLast.o)
...generate md5sums for $^...
xxxLast.o $(compiled_objs-but-not-xxxLast.o): $(obj_dir)/%.o: $(src_base)/%.cpp