I get a similar error message when attempting to install ldc in Ubuntu Precise.
The following packages have unmet dependencies:
ldc : Depends: libllvm2.7 but it is not installable
Recommends: libtango-ldc-dev but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
Thanks for reporting this issue.
I get a similar error message when attempting to install ldc in Ubuntu Precise.
The following packages have unmet dependencies:
ldc : Depends: libllvm2.7 but it is not installable
Recommends: libtango-ldc-dev but it is not going to be installed
E: Unable to correct problems, you have held broken packages.