In the first bunker the frame rate drops heavily and stutters in spots, the
frame rate is perfect 60fps before and after this area.  I tested the same area
on Windows 10 and also Ubuntu with proprietary drivers and they don't suffer
from this issue.  

Tested using Proton 3.7-6 as the game needs a patched wine to run. Hopefully
the trace is long enough to see the issue as the frame rate drop doesn't always
happen immediately.

Apitrace:
https://drive.google.com/file/d/1LWRVhJMeXo0h8IbUFBwj8vyTyyml6R5k/view?usp=sharing

Video showing the issue:
https://youtu.be/WheSQWf09yM

-Arch Linux
-RX Vega 56/Ryzen 1700
-mesa 18.3-git