xmonad cannot be built on natty

Binary package hint: xmonad

I suspect a (hopefully simple?) build-dependency issue and/or incompatibilities with related packages.

First the following build-dep packages are not available in the repository:
# apt-get build-dep xmonad
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages have unmet dependencies:
 libghc6-x11-dev : Depends: libghc6-base-dev-4.2.0.0-2cc27 but it is not installable
                   Depends: libghc6-syb-dev-0.1.0.2-3787e but it is not installable
 libghc6-x11-prof : Depends: libghc6-base-prof-4.2.0.0-2cc27 but it is not installable
                    Depends: libghc6-syb-prof-0.1.0.2-3787e but it is not installable
E: Build-dependencies for xmonad could not be satisfied.

after manually building, packaging and installing:
> libghc6-x11-dev
> libghc6-x11-prof

# apt-get build-dep xmonad
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
  libghc6-mtl-dev libghc6-mtl-prof
[...]
finishes without dependency problems

xmonad-0.9.1 # dpkg-buildpackage -b
dpkg-buildpackage: export CFLAGS from dpkg-buildflags (origin: vendor): -g -O2
dpkg-buildpackage: export CPPFLAGS from dpkg-buildflags (origin: vendor):
dpkg-buildpackage: export CXXFLAGS from dpkg-buildflags (origin: vendor): -g -O2
dpkg-buildpackage: export FFLAGS from dpkg-buildflags (origin: vendor): -g -O2
dpkg-buildpackage: export LDFLAGS from dpkg-buildflags (origin: vendor): -Wl,-Bsymbolic-functions
dpkg-buildpackage: source package xmonad
dpkg-buildpackage: source version 0.9.1-2build2
dpkg-buildpackage: source changed by Iain Lane <email address hidden>
dpkg-buildpackage: host architecture amd64
 dpkg-source --before-build xmonad-0.9.1
 debian/rules clean
test -x debian/rules
dh_testroot
dh_clean
[ ! -x "debian/hlibrary.setup" ] || debian/hlibrary.setup clean
cleaning...
rm -rf dist dist-ghc6 dist-hugs debian/hlibrary.setup Setup.hi Setup.ho Setup.o .*config*
rm -f build-ghc6-stamp build-hugs-stamp build-haddock-stamp
rm -rf debian/tmp-inst-ghc6
rm -f debian/hlibrary.Makefile
rm -rf debian/dh_haskell_shlibdeps
 debian/rules build
test -x debian/rules
mkdir -p "."
/usr/share/cdbs/1/rules/buildcore.mk:104: WARNING: DEB_COMPRESS_EXCLUDE is a deprecated variable
if test ! -e Setup.lhs -a ! -e Setup.hs; then echo "No setup script found!"; exit 1; fi
for setup in Setup.lhs Setup.hs; do if test -e $setup; then ghc6 --make $setup -o debian/hlibrary.setup; exit 0; fi; done
[1 of 1] Compiling Main ( Setup.lhs, Setup.o )
Linking debian/hlibrary.setup ...
debian/hlibrary.setup configure --ghc -v2 \
  --prefix=/usr --libdir=/usr/lib/haskell-packages/ghc6/lib \
  --builddir=dist-ghc6 \
  --haddockdir=/usr/lib/ghc-6.12.3/haddock/xmonad-0.9.1/ \
  --htmldir=/usr/share/doc/libghc6-xmonad-doc/html/ --enable-library-profiling \

Configuring xmonad-0.9.1...
Flags chosen: testing=False, small_base=True
Dependency X11 >=1.5.0.0 && <1.6: using X11-1.5.0.0
Dependency base ==3.*: using base-3.0.3.2
Dependency containers -any: using containers-0.3.0.0
Dependency directory -any: using directory-1.0.1.1
Dependency filepath -any: using filepath-1.1.0.4
Dependency mtl -any: using mtl-1.1.0.2
Dependency process -any: using process-1.0.1.3
Dependency unix -any: using unix-2.4.0.2
Using Cabal-1.8.0.6 compiled by ghc-6.12
Using compiler: ghc-6.12.3
Using install prefix: /usr
Binaries installed in: /usr/bin
Libraries installed in:
/usr/lib/haskell-packages/ghc6/lib/xmonad-0.9.1/ghc-6.12.3
Private binaries installed in: /usr/libexec
Data files installed in: /usr/share/xmonad-0.9.1
Documentation installed in: /usr/share/doc/xmonad-0.9.1
No alex found
Using ar found on system at: /usr/bin/ar
No c2hs found
No cpphs found
No ffihugs found
Using gcc version 4.5.2 found on system at: /usr/bin/gcc
Using ghc version 6.12.3 found on system at: /usr/bin/ghc
Using ghc-pkg version 6.12.3 found on system at: /usr/bin/ghc-pkg
No greencard found
Using haddock version 2.6.1 found on system at: /usr/bin/haddock
No happy found
No hmake found
Using hsc2hs version 0.67 found on system at: /usr/bin/hsc2hs
Using hscolour version 1.16 found on system at: /usr/bin/HsColour
No hugs found
No jhc found
Using ld found on system at: /usr/bin/ld
No lhc found
No lhc-pkg found
No nhc98 found
Using pkg-config version 0.25 found on system at: /usr/bin/pkg-config
Using ranlib found on system at: /usr/bin/ranlib
Using strip found on system at: /usr/bin/strip
Using tar found on system at: /bin/tar
debian/hlibrary.setup build --builddir=dist-ghc6
Preprocessing library xmonad-0.9.1...
Preprocessing executables for xmonad-0.9.1...
Building xmonad-0.9.1...
<command line>: cannot satisfy -package-id X11-1.5.0.0-e303e9e71d3b6055d5c970517461f343
    (use -v for more information)
make: *** [build-ghc6-stamp] Error 1
dpkg-buildpackage: error: debian/rules build gave error exit status 2