Change hardcoded path to tzdata directory

[Petar]

On Saturday, 22 December 2018 at 17:55:25 UTC, kinke wrote:
> [..]
> 
> Your PR was merged into master, not stable, which means chances 
> are this isn't going to land before 2.085, so you'll have to 
> adapt LDC's Phobos until then.

That change was merged quite a while ago, so it was part of DMD 
2.079 and LDC 1.9 - see: 
https://github.com/ldc-developers/phobos/commit/735b360c4215720adf3b64b76c274ce1094538f9#diff-fdecdaf8196f65e06e550af5fd31a088.

On related note, I have observed several times at least where 
changes to the build system upstream weren't propagated 
downstream to GDC and LDC as you guys are using different build 
systems. The -dipxxxx and -transition=xxxxx flags look like 
future trouble maker candidates. Any suggestions how we could 
make this easier for you?