POSIX make really does make auto dependencies hard, but GNU make actually solves this fairly cleanly by adding an include directive. As long as you have a script or program to process a file and spit out its dependencies in make style (e.g., GCC does this for C and C++ with its -M flags), you can just include the outputs of that process and make will do the rest.

For example, here's how I handle a simple C project.

    CSRC := [list .c files here]
    DEPS := $(CSRC:.c=.d)
    
    [standard statements for building go here]
    
    %.d: %.c
            gcc -MM -MF $@ $<
    
    -include $(DEPS)

Poof. Automatic dependency handling. You can see how any sort of dependency that can be detected by some sort of preprocessor can be plugged in here.