Debian – How to block a package installation on Debian

Your system is boned in some very curious way. If ldconfig is the cause of a post-installation script returning 135, it's because ldconfig is dying with a SIGFPE -- a floating point exception. That either points to a very curious bug in ldconfig (very unlikely) or some sort of latent hardware error (far more likely).

If you'd like to diagnose this problem further, you can try running ldconfig in a debugger and see what happens, but there isn't going to be a quick fix to this, and my money's still on a hardware fault.

Install the equivs package.

That will let you create trivial packages that fulfill the dependency. In this case, you'll create a fake package providing httpd.

Here is an article on how to do this task.

Although, as @Holger says, the best thing to do is install lighttpd from the debian repository as it provides httpd.