I have reported this on AMD forums countless times. 7-8 drivers have gone by which still report the presence of this extension erronously. In case you wish to use ComputeCpp with AMD GPUs, 18.2.3 is the last driver to support SPIR.
Also do note, that 18.2.3 still shows the CPU device, but in fact it’s not functioning. Trying to compile any OpenCL kernel results in internal compiler errors. CPU runtime last worked sometime around 17.7, but that is too old for many newer GPUs, such as my RX 580. Should you want to join the “conversation” on AMD forums, you can do so [here].