libapache2-mod-authn-yubikey: FTBFS: make[1]: *** No rule to make target `../../apache228-install/build/special.mk'. Stop.

Imported from Debian bug http://bugs.debian.org/725536:

Source: libapache2-mod-authn-yubikey
Version: 1.0-1.1
Severity: serious
Tags: jessie sid
User: <email address hidden>
Usertags: qa-ftbfs-20131006 qa-ftbfs
Justification: FTBFS on amd64

Hi,

During a rebuild of all packages in sid, your package failed to build on
amd64.

Relevant part (hopefully):
> fakeroot debian/rules clean
> dh clean --with apache2
> dh_testdir
> dh_auto_clean
> make[1]: Entering directory `/«PKGBUILDDIR»'
> Makefile:9: ../../apache228-install/build/special.mk: No such file or directory
> make[1]: *** No rule to make target `../../apache228-install/build/special.mk'. Stop.
> make[1]: Leaving directory `/«PKGBUILDDIR»'
> dh_auto_clean: make -j1 distclean returned exit code 2
> make: *** [clean] Error 2

The full build log is available from:
   http://aws-logs.debian.net/ftbfs-logs/2013/10/06/libapache2-mod-authn-yubikey_1.0-1.1_unstable.log

A list of current common problems and possible solutions is available at
http://wiki.debian.org/qa.debian.org/FTBFS . You're welcome to contribute!

About the archive rebuild: The rebuild was done on EC2 VM instances from
Amazon Web Services, using a clean, minimal and up-to-date chroot. Every
failed build was retried once to eliminate random failures.