Yea, that does sound "not too easy".
AMD has their OpenCL support in the Catalyst driver
When I tried it last time with fglrx it was not in the driver (at least not the opencl libraries) but I had to install the amd stream sdk (now app sdk?). And that was literally the only thing I had to do, opencl programs would just work after that.
Didn't you want to write something additionally to that... I mean, why it's worse off?
Intel has the Beignet project for open-source OpenCL but that's even worse off than the Gallium3D OpenCL support.
I wanted to try beignet so I fixed some includes that got moved from llvm/* to llvm/IR/*, but then...
What a letdown.
#error "Only LLVM 3.0 / 3.1 is supported"