g++ include all /usr/include recursively

#include <gtkmm.h>

# Makefile
ifeq ($(shell pkg-config --modversion gtkmm-2.4),)
  $(error Package gtkmm-2.4 needed to compile)
endif

CXXFLAGS += `pkg-config --cflags gtkmm-2.4`
LDLIBS += `pkg-config --libs gtkmm-2.4`

BINS = program
program_OBJS = a.o b.o c.o

all: $(BINS)

program: $(program_OBJS)
        $(CXX) $(LDFLAGS) $^ $(LOADLIBES) $(LDLIBS) -o $@

# this part is actually optional, since it's covered by gmake's implicit rules
%.o: %.cc
        $(CXX) -c $(CPPFLAGS) $(CXXFLAGS) $< -o $@

pkg-config --cflags --libs gtkmm-2.4

#include <gtkmm-2.4/gtkmm.h>

INC=-I/usr/include/gtkmm-2.4/

helloworld: helloworld.o
    g++ -o $@ $<

helloworld.o: helloworld.c
    g++ $(INC) -c -o $@ $<

.PHONY: clean

clean:
    rm -f helloworld helloworld.o