with debug output:

ubuntu@ubuntu:~$ sudo apt-get install -o Debug::pkgProblemResolver=true cpp:i386
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Starting
Starting 2
Investigating (0) x11-xserver-utils [ amd64 ] < 7.6+3 > ( x11 )
Broken x11-xserver-utils:amd64 Depends on cpp [ amd64 ] < 4:4.6.1-2ubuntu5 > ( interpreters )
  Considering cpp:amd64 5 as a solution to x11-xserver-utils:amd64 8
  Added cpp:amd64 to the remove list
  Fixing x11-xserver-utils:amd64 via keep of cpp:amd64
Investigating (0) cpp [ amd64 ] < 4:4.6.1-2ubuntu5 > ( interpreters )
Broken cpp:amd64 Depends on cpp-4.6 [ amd64 ] < 4.6.2-5ubuntu1 > ( interpreters ) (>= 4.6.1-1)
  Considering cpp-4.6:amd64 1 as a solution to cpp:amd64 5
  Added cpp-4.6:amd64 to the remove list
Broken cpp:amd64 Conflicts on cpp [ i386 ] < none -> 4:4.6.1-2ubuntu5 > ( interpreters )
  Considering cpp:i386 9999 as a solution to cpp:amd64 5
  Removing cpp:amd64 rather than change cpp:i386
Investigating (0) x11-apps [ amd64 ] < 7.6+5 > ( x11 )
Broken x11-apps:amd64 Depends on cpp [ amd64 ] < 4:4.6.1-2ubuntu5 > ( interpreters )
  Considering cpp:amd64 5 as a solution to x11-apps:amd64 2
  Removing x11-apps:amd64 rather than change cpp:amd64
Investigating (0) gcc-4.6 [ amd64 ] < 4.6.2-5ubuntu1 > ( devel )
Broken gcc-4.6:amd64 Depends on cpp-4.6 [ amd64 ] < 4.6.2-5ubuntu1 > ( interpreters ) (= 4.6.2-5ubuntu1)
  Considering cpp-4.6:amd64 1 as a solution to gcc-4.6:amd64 2
  Added cpp-4.6:amd64 to the remove list
  Fixing gcc-4.6:amd64 via keep of cpp-4.6:amd64
Investigating (0) x11-session-utils [ amd64 ] < 7.6+1ubuntu1 > ( x11 )
Broken x11-session-utils:amd64 Depends on cpp [ amd64 ] < 4:4.6.1-2ubuntu5 > ( interpreters )
  Considering cpp:amd64 5 as a solution to x11-session-utils:amd64 2
  Removing x11-session-utils:amd64 rather than change cpp:amd64
Investigating (0) libidl0 [ amd64 ] < 0.8.14-0.2 > ( libs )
Broken libidl0:amd64 Depends on cpp [ amd64 ] < 4:4.6.1-2ubuntu5 > ( interpreters )
  Considering cpp:amd64 5 as a solution to libidl0:amd64 2
  Removing libidl0:amd64 rather than change cpp:amd64
Investigating (0) liborbit2 [ amd64 ] < 1:2.14.19-0.1 > ( libs )
Broken liborbit2:amd64 Depends on libidl0 [ amd64 ] < 0.8.14-0.2 > ( libs )
  Considering libidl0:amd64 2 as a solution to liborbit2:amd64 2
  Removing liborbit2:amd64 rather than change libidl0:amd64
Investigating (0) libreoffice-gnome [ amd64 ] < 1:3.4.4-0ubuntu2 > ( gnome )
Broken libreoffice-gnome:amd64 Depends on liborbit2 [ amd64 ] < 1:2.14.19-0.1 > ( libs ) (>= 1:2.14.10)
  Considering liborbit2:amd64 2 as a solution to libreoffice-gnome:amd64 1
  Removing libreoffice-gnome:amd64 rather than change liborbit2:amd64
Investigating (0) gcc [ amd64 ] < 4:4.6.1-2ubuntu5 > ( devel )
Broken gcc:amd64 Depends on cpp [ amd64 ] < 4:4.6.1-2ubuntu5 > ( interpreters ) (>= 4:4.6.1-2ubuntu5)
  Considering cpp:amd64 5 as a solution to gcc:amd64 1
  Removing gcc:amd64 rather than change cpp:amd64
Investigating (0) xorg [ amd64 ] < 1:7.6+7ubuntu7 > ( x11 )
Broken xorg:amd64 Depends on x11-apps [ amd64 ] < 7.6+5 > ( x11 )
  Considering x11-apps:amd64 2 as a solution to xorg:amd64 1
  Removing xorg:amd64 rather than change x11-apps:amd64
Investigating (0) cpp-4.6 [ amd64 ] < 4.6.2-5ubuntu1 > ( interpreters )
Broken cpp-4.6:amd64 Conflicts on cpp-4.6 [ i386 ] < none -> 4.6.2-5ubuntu1 > ( interpreters )
  Considering cpp-4.6:i386 1 as a solution to cpp-4.6:amd64 1
  Removing cpp-4.6:amd64 rather than change cpp-4.6:i386
Investigating (0) ubuntu-desktop [ amd64 ] < 1.253 > ( metapackages )
Broken ubuntu-desktop:amd64 Depends on xorg [ amd64 ] < 1:7.6+7ubuntu7 > ( x11 )
  Considering xorg:amd64 1 as a solution to ubuntu-desktop:amd64 0
  Removing ubuntu-desktop:amd64 rather than change xorg:amd64
Investigating (1) x11-xserver-utils [ amd64 ] < 7.6+3 > ( x11 )
Broken x11-xserver-utils:amd64 Depends on cpp [ amd64 ] < 4:4.6.1-2ubuntu5 > ( interpreters )
  Considering cpp:amd64 5 as a solution to x11-xserver-utils:amd64 8
  Added cpp:amd64 to the remove list
  Fixing x11-xserver-utils:amd64 via keep of cpp:amd64
Investigating (1) cpp [ amd64 ] < 4:4.6.1-2ubuntu5 > ( interpreters )
Broken cpp:amd64 Depends on cpp-4.6 [ amd64 ] < 4.6.2-5ubuntu1 > ( interpreters ) (>= 4.6.1-1)
  Considering cpp-4.6:amd64 1 as a solution to cpp:amd64 5
  Added cpp-4.6:amd64 to the remove list
Broken cpp:amd64 Conflicts on cpp [ i386 ] < none -> 4:4.6.1-2ubuntu5 > ( interpreters )
  Considering cpp:i386 9999 as a solution to cpp:amd64 5
  Removing cpp:amd64 rather than change cpp:i386
Investigating (1) gcc-4.6 [ amd64 ] < 4.6.2-5ubuntu1 > ( devel )
Broken gcc-4.6:amd64 Depends on cpp-4.6 [ amd64 ] < 4.6.2-5ubuntu1 > ( interpreters ) (= 4.6.2-5ubuntu1)
  Considering cpp-4.6:amd64 1 as a solution to gcc-4.6:amd64 2
  Added cpp-4.6:amd64 to the remove list
  Fixing gcc-4.6:amd64 via keep of cpp-4.6:amd64
Investigating (1) cpp-4.6 [ amd64 ] < 4.6.2-5ubuntu1 > ( interpreters )
Broken cpp-4.6:amd64 Conflicts on cpp-4.6 [ i386 ] < none -> 4.6.2-5ubuntu1 > ( interpreters )
  Considering cpp-4.6:i386 1 as a solution to cpp-4.6:amd64 1
  Removing cpp-4.6:amd64 rather than change cpp-4.6:i386
Investigating (2) x11-xserver-utils [ amd64 ] < 7.6+3 > ( x11 )
Broken x11-xserver-utils:amd64 Depends on cpp [ amd64 ] < 4:4.6.1-2ubuntu5 > ( interpreters )
  Considering cpp:amd64 5 as a solution to x11-xserver-utils:amd64 8
  Added cpp:amd64 to the remove list
  Fixing x11-xserver-utils:amd64 via keep of cpp:amd64
Investigating (2) cpp [ amd64 ] < 4:4.6.1-2ubuntu5 > ( interpreters )
Broken cpp:amd64 Depends on cpp-4.6 [ amd64 ] < 4.6.2-5ubuntu1 > ( interpreters ) (>= 4.6.1-1)
  Considering cpp-4.6:amd64 1 as a solution to cpp:amd64 8
  Added cpp-4.6:amd64 to the remove list
Broken cpp:amd64 Conflicts on cpp [ i386 ] < none -> 4:4.6.1-2ubuntu5 > ( interpreters )
  Considering cpp:i386 9999 as a solution to cpp:amd64 8
  Removing cpp:amd64 rather than change cpp:i386
Investigating (2) gcc-4.6 [ amd64 ] < 4.6.2-5ubuntu1 > ( devel )
Broken gcc-4.6:amd64 Depends on cpp-4.6 [ amd64 ] < 4.6.2-5ubuntu1 > ( interpreters ) (= 4.6.2-5ubuntu1)
  Considering cpp-4.6:amd64 1 as a solution to gcc-4.6:amd64 2
  Added cpp-4.6:amd64 to the remove list
  Fixing gcc-4.6:amd64 via keep of cpp-4.6:amd64
Investigating (2) cpp-4.6 [ amd64 ] < 4.6.2-5ubuntu1 > ( interpreters )
Broken cpp-4.6:amd64 Conflicts on cpp-4.6 [ i386 ] < none -> 4.6.2-5ubuntu1 > ( interpreters )
  Considering cpp-4.6:i386 1 as a solution to cpp-4.6:amd64 2
  Added cpp-4.6:i386 to the remove list
  Fixing cpp-4.6:amd64 via keep of cpp-4.6:i386
Investigating (3) cpp [ i386 ] < none -> 4:4.6.1-2ubuntu5 > ( interpreters )
Broken cpp:i386 Depends on cpp-4.6 [ i386 ] < none -> 4.6.2-5ubuntu1 > ( interpreters ) (>= 4.6.1-1)
  Considering cpp-4.6:i386 2 as a solution to cpp:i386 9999
  Re-Instated cpp-4.6:i386
Investigating (3) x11-xserver-utils [ amd64 ] < 7.6+3 > ( x11 )
Broken x11-xserver-utils:amd64 Depends on cpp [ amd64 ] < 4:4.6.1-2ubuntu5 > ( interpreters )
  Considering cpp:amd64 9999 as a solution to x11-xserver-utils:amd64 8
  Removing x11-xserver-utils:amd64 rather than change cpp:amd64
Investigating (3) acpi-support [ amd64 ] < 0.138 > ( admin )
Broken acpi-support:amd64 Depends on x11-xserver-utils [ amd64 ] < 7.6+3 > ( x11 )
  Considering x11-xserver-utils:amd64 9999 as a solution to acpi-support:amd64 1
  Removing acpi-support:amd64 rather than change x11-xserver-utils:amd64
Investigating (3) cpp-4.6 [ amd64 ] < 4.6.2-5ubuntu1 > ( interpreters )
Broken cpp-4.6:amd64 Conflicts on cpp-4.6 [ i386 ] < none -> 4.6.2-5ubuntu1 > ( interpreters )
  Considering cpp-4.6:i386 2 as a solution to cpp-4.6:amd64 2
  Removing cpp-4.6:amd64 rather than change cpp-4.6:i386
Investigating (4) gcc-4.6 [ amd64 ] < 4.6.2-5ubuntu1 > ( devel )
Broken gcc-4.6:amd64 Depends on cpp-4.6 [ amd64 ] < 4.6.2-5ubuntu1 > ( interpreters ) (= 4.6.2-5ubuntu1)
  Considering cpp-4.6:amd64 2 as a solution to gcc-4.6:amd64 2
  Removing gcc-4.6:amd64 rather than change cpp-4.6:amd64
Done
The following extra packages will be installed:
  cpp-4.6:i386 gcc-4.6-base:i386 libc-bin:i386 libc6 libc6:i386 libgcc1:i386 libgmp10:i386 libmpc2:i386 libmpfr4:i386 zlib1g:i386
Suggested packages:
  cpp-doc:i386 gcc-4.6-locales:i386 glibc-doc glibc-doc:i386
The following packages will be REMOVED:
  acpi-support cpp cpp-4.6 gcc gcc-4.6 libc-bin libidl0 liborbit2 libreoffice-gnome ubuntu-desktop x11-apps x11-session-utils x11-xserver-utils
  xorg
The following NEW packages will be installed:
  cpp:i386 cpp-4.6:i386 gcc-4.6-base:i386 libc-bin:i386 libc6:i386 libgcc1:i386 libgmp10:i386 libmpc2:i386 libmpfr4:i386 zlib1g:i386
The following packages will be upgraded:
  libc6
WARNING: The following essential packages will be removed.
This should NOT be done unless you know exactly what you are doing!
  libc-bin
1 upgraded, 10 newly installed, 14 to remove and 0 not upgraded.
Need to get 14.5 MB of archives.
After this operation, 10.6 MB disk space will be freed.
You are about to do something potentially harmful.
To continue type in the phrase 'Yes, do as I say!'
 ?] no