`clEnqueueFillBuffer` is part of OpenCL 1.2 [1] [2].

Mesa claims to support OpenCL 1.2:
```
# grep -B1 CL_VERSION /usr/include/CL/cl.h
/* OpenCL Version */
#define CL_VERSION_1_0                              1
#define CL_VERSION_1_1                              1
#define CL_VERSION_1_2                              1
```

It declares `clEnqueueFillBuffer`:
```
# grep -B1 -A8 clEnqueueFillBuffer /usr/include/CL/cl.h
extern CL_API_ENTRY cl_int CL_API_CALL
clEnqueueFillBuffer(cl_command_queue   /* command_queue */,
                    cl_mem             /* buffer */, 
                    const void *       /* pattern */, 
                    size_t             /* pattern_size */, 
                    size_t             /* offset */, 
                    size_t             /* size */, 
                    cl_uint            /* num_events_in_wait_list */, 
                    const cl_event *   /* event_wait_list */, 
                    cl_event *         /* event */) CL_API_SUFFIX__VERSION_1_2;
```

But does not define it:
```
# scanelf -s clEnqueueFillBuffer /usr/lib/libOpenCL.so
 TYPE   SYM FILE 
ET_DYN  -  /usr/lib/libOpenCL.so 
```

Logically, it also seems to be missing in the API dispatcher [1].

I assume Mesa should not claim to support OpenCL 1.2 via `CL_VERSION_1_2`, if at least one of the OpenCL 1.2 functions is not implemented.

[1]: https://www.khronos.org/registry/cl/sdk/1.2/docs/man/xhtml/clEnqueueFillBuffer.html
[2]: https://www.khronos.org/registry/cl/specs/opencl-1.2.pdf#page=85
[3]: http://cgit.freedesktop.org/mesa/mesa/tree/src/gallium/state_trackers/clover/api/dispatch.cpp#n129