Unable to set the backend to opencl

I use the following driver for my card with mesa-opencl-icd loader and radeon driver.
```
0d:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI] Sun XT [Radeon HD 8670A/8670M/8690M / R5 M330 / M430 / Radeon 520 Mobile] (rev 83)
Subsystem: Hewlett-Packard Company Sun XT [Radeon HD 8670A/8670M/8690M / R5 M330 / M430 / Radeon 520 Mobile]
```
Installed Arrayfire and made sure that all the libraries are loaded. Using the ArrayFire.jl, arrayfire loads in Julia perfectly and runs on my AMD card.
```
ArrayFire v3.7.1 (OpenCL, 64-bit Linux, build d9d9b65)
[0] Clover: AMD HAINAN (DRM 2.50.0, 5.4.0-33-generic, LLVM 9.0.1), 2048 MB
```
But, in my Python the array fire loads with the following info:
```
ArrayFire v3.7.1 (CPU, 64-bit Linux, build d9d9b65)
[0] Intel: Intel(R) Core(TM) i3-5010U CPU @ 2.10GHz
```
I also use the following in my .bashrc to update my environment:
```
export LD_LIBRARY_PATH=/opt/arrayfire/lib64:$LD_LIBRARY_PATH
```
When I try to change the backend, I get the following error:
```
>>> af.set_backend('opencl')
Traceback (most recent call last):
File "", line 1, in
File "/home/saipavanchitta/.local/lib/python3.8/site-packages/arrayfire/library.py", line 658, in set_backend
raise RuntimeError("Can not change backend to %s after loading %s" % (name, backend.name()))
RuntimeError: Can not change backend to opencl after loading cpu
```
Is there something that I am missing?

Reproduce the Python import and af.set_backend('opencl') sequence, then inspect arrayfire/library.py around set_backend at line 658 and the backend-loading path. Compare the Python behavior with the reported ArrayFire.jl OpenCL load; done means the Python sequence no longer raises the reported RuntimeError and a regression test covers it.

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