In fact this was an existing issue when exceeding the number of available
closure, but it's more common now that we set the number to 0 for shadows
and emission
With a Titan Xp, reduces path trace local memory from 1092MB to 840MB.
Benchmark performance was within 1% with both RX 480 and Titan Xp.
Original patch was implemented by Sergey.
Differential Revision: https://developer.blender.org/D2249
While this compiler is not officially supported yet, getting it to work is
a nice thing because more and more AMD cards will fall under MESA driver.
It's also nice to use explicit comparison with NULL, which makes it more
clear whether variable is a boolean or pointer. Even Rust enforces this!
Patch by Ian Bruce with own modifications.
