cat > 'test.c' <<'EOF'
#include <stdio.h>
#include <mynumber.h>
int main()
{
        printf("NUMBER is %d\n", NUMBER);
        return 0;
}
EOF
cat > 'Makefile.omk' <<'EOF'
bin_PROGRAMS = test

test_SOURCES = test.c

INCLUDES = -I$(SOURCES_DIR)/inc
EOF
mkdir 'inc'
echo '#define NUMBER 456' > 'inc/mynumber.h'