It what I thought but I tried this morning unsuccessfully:

$ LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/include/httrack
$ export LD_LIBRARY_PATH
$ echo $LD_LIBRARY_PATH 
:/usr/include/httrack
$ gcc -O -g3 -Wall -D_REENTRANT -shared -o mycallback.so test.c -lhttrack2            

test.c:6: fatal error: httrack-library.h: No such file or directory
compilation terminated.


Is this what you meant ?