llvm-3.9 travis build is failing

[bscarlet]

• The travis build is failing because travis can't install the llvm-3.9-dev package.
• Travis can't install the llvm-3.9-dev package because it's configured in .travis.yml to use the "llvm-toolchain-precise" distribution, which currently contains not 3.9 but 4.0 packages.
• The "llvm-toolchain-precise-3.9" distribution ought to contain llvm-3.9-dev package, but doesn't
• The "llvm-toolchain-precise-3.9" distribution is currently empty, because the jenkins build which populates it is failing
• The jenkins build fails with objcopy: unrecognized option '--extract-dwo'
• objcopy does not recognize "--extract-dwo" because binutils on precise is old
• There is an llvm bug for the failure to happen earlier at configure time instead of build time, but as yet there seems to be none for the jenkins build failure itself.

[cocreature]

Even if llvm-toolchain-precise-3.9 would contain the necessary packages, we can’t use it because the travis container builds can only install packages from whitelisted repositories and this repo is not yet whitelisted.

[bscarlet]

We could switch to building & caching LLVM ourselves, I suppose.

[cocreature]

Yeah we could do that, but I assume that when LLVM-3.9 is released they’ll publish binary packages so we can probably just download them, unpack & set the path appropriately and thereby avoid having to build it ourselves.

[cocreature]

But if that doesn’t happen in the next few days we should definitely build it ourselves.