Compile pam with pam_cracklib.so

pam_cracklib.so is dependent on libcrack.so. Configure command will search libcrack.so. If it didn't find it, configure will disable pam_cracklib.so module. So it won't be compiled. For cross-compiling or libcrack.so is in non-standard directories, configure pam with LDFLAGS=-L$(path-to-libcrack.so).