Comment 0 for bug 1171340

In order to land llvm-3.2, dh-exec needs to be upgraded to 0.4 or newer. dh-exec is a build helper, and should have no backwards compatability issues.

llvm-3.2 will be a new package only to be used for mesa-lts-raring, so there is no regression potential for that.

Updating libdrm will require more thought. While the API is stable and I haven't noticed any new bugs being introduced, I fear that bumping the version number to beyond what quantal provides will make upgrading to quantal harder. Unfortunately, I think this is the only solution.

The ubuntu-x-swat/x-updates ppa was recommended to be enabled for steam, and was already providing a newer libdrm:
https://launchpad.net/~ubuntu-x-swat/+archive/x-updates/+packages

The only way out I see is removing libdrm from that ppa, pushing a newer libdrm version to precise, removing libdrm from that ppa, and make update-manager downgrade libdrm during an upgrade to quantal.