Supporting LLVM 3.5 and 3.6

[Johan Engelen via digitalmars-d-ldc]

Hi all,
   We now support 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 5.0 ... that's 7 
versions of LLVM, quite a bunch!

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.

cheers,
   Johan