Fail when LLVM 3.6 is detected; disable Travis builds accordingly

[dnadlinger]

No description provided.

[dnadlinger]

@redstar: This seems to be just about the only thing we can do for now, unless we want to try adding crazy workarounds to our IR gen. Any ideas?

[redstar]

The linker class is in a single file. We could include the fixed class and use it if we detect LLVM 3.6.

[dnadlinger]

…unless somebody tries to use a shared library build of LLVM?

[dnadlinger]

(My favourite option for now is just to get rid of Linker entirely and emit everything to the same module for -singleobj builds.)

[dnadlinger]

Oh, you mean, we could just ship our own ldc::IRLinker instead? Yes, that would probably be the easiest fix. However, I'll still try to get rid of it entirely tomorrow. It's a big source of complexity I'd rather not have in the first place.

[dnadlinger]

See #974 which removes the dependency on llvm::Linker (except for inline IR, where it is not problematic).

[redstar]

Yes, I proposed to include the modified llvm::Linker class. But removing the dependency on llvm::Linker is another good solution. :-)