Supporting LLVM 3.5 and 3.6

[kinke via digitalmars-d-ldc]

On Friday, 14 July 2017 at 11:49:13 UTC, Johan Engelen wrote:
> How long do we want to keep supporting LLVM 3.5 and 3.6? Can we 
> remove support from LDC >= 1.4?
>
> Not that it is bothering me a whole lot, but for example 
> looking at the debuginfo code is annoying with all the 
> #ifdef'ing.
> Culling 3.5 and 3.6 support would also save a bit of TravisCI 
> time.

Fine with me. Ubuntu 14.04 is still on unsupported LLVM 3.4, 
16.04 already on LLVM 3.8, and SPIR-V apparently not restricted 
to 3.6 anymore.