Currently ENABLE_GPU_PROCESS is XCode only. That should be changed so other ports can implement.
Created attachment 388478 [details] WIP Patch Adding the common changes for ENABLE_GPU_PROCESS. Alex or anyone else over at Apple can you take a look at the Mac CMake port and see if this possibly builds?
I'm not opposed to this, but the GPU Process development is currently quite experimental, and I don't want to add the burden of keeping the build working on other ports. I'm ok with this being in the repository but disabled by default.
*** This bug has been marked as a duplicate of bug 208866 ***