├── Makefile
└── src
    ├── folder1
    │   ├── somefiles.c
    │   └── somefiles.h
    ├── folder2
    │   ├── problematic.h
    │   ├── somefiles.c
    │   ├── somefiles.h
    │   └── subdir
    │       └── included_file.h
    └── folder3
        ├── somefiles.c
        └── somefiles.h

LIBRARY_INC_PATHS     = $(addprefix -I, $(shell find . -name '*.h' -printf '"%h"n' | sort -u))

#include "subdir/included_file.h"

#include "included_file.h"