Unable to build with CUDA backend for NVIDIA Jetson

**Describe the bug**
I am attempting to build DPC++ with CUDA backend for a Jetson TX2 that is running Ubuntu 18.04. The CPUs are AARCH64, but I'm only interested in the CUDA backend.

Eventually, the build will fail with:
`error: unable to create target: 'No available targets are compatible with triple "aarch64-unknown-linux-gnu"'`

**To Reproduce**
Please describe the steps to reproduce the behavior:

Run the following on a Jetson TX2:

```
python $DPCPP_HOME/llvm/buildbot/configure.py --cuda --no-werror
python $DPCPP_HOME/llvm/buildbot/compile.py

```

1. Include code snippet as short as possible: N/A
2. Specify the command which should be used to compile the program: See above
3. Specify the comment which should be used to launch the program: N/A
4. Indicate what is wrong and what was expected

The build eventually fails with:

```
$ python $DPCPP_HOME/llvm/buildbot/compile.py
args:Namespace(base_branch=None, branch=None, build_number=None, build_parallelism=None, builder_dir=None, obj_dir=None, pr_number=None, src_dir=None)
[Cmake Command]: cmake --build /home/user/sycl_workspace/llvm/build -- deploy-sycl-toolchain deploy-opencl-aot -j 4
[1/649] Generating ../../lib/libsycl-crt.o
FAILED: lib/libsycl-crt.o
cd /home/user/sycl_workspace/llvm/build/tools/libdevice && /home/user/sycl_workspace/llvm/build/bin/clang-13 -fsycl -c -Wno-sycl-strict -Wno-undefined-internal -sycl-std=2017 -fsycl-targets=spir64_x86_64-unknown-unknown-sycldevice,spir64_gen-unknown-unknown-sycldevice,spir64_fpga-unknown-unknown-sycldevice,spir64-unknown-unknown-sycldevice /home/user/sycl_workspace/llvm/libdevice/crt_wrapper.cpp -o /home/user/sycl_workspace/llvm/build/lib/libsycl-crt.o
error: unable to create target: 'No available targets are compatible with triple "aarch64-unknown-linux-gnu"'
1 error generated.
[2/649] Generating ../../lib/libsycl-complex.o
FAILED: lib/libsycl-complex.o
cd /home/user/sycl_workspace/llvm/build/tools/libdevice && /home/user/sycl_workspace/llvm/build/bin/clang-13 -fsycl -c -Wno-sycl-strict -Wno-undefined-internal -sycl-std=2017 -fsycl-targets=spir64_x86_64-unknown-unknown-sycldevice,spir64_gen-unknown-unknown-sycldevice,spir64_fpga-unknown-unknown-sycldevice,spir64-unknown-unknown-sycldevice /home/user/sycl_workspace/llvm/libdevice/complex_wrapper.cpp -o /home/user/sycl_workspace/llvm/build/lib/libsycl-complex.o
error: unable to create target: 'No available targets are compatible with triple "aarch64-unknown-linux-gnu"'
1 error generated.
[3/649] Generating ../../lib/libsycl-complex-fp64.o
FAILED: lib/libsycl-complex-fp64.o
cd /home/user/sycl_workspace/llvm/build/tools/libdevice && /home/user/sycl_workspace/llvm/build/bin/clang-13 -fsycl -c -Wno-sycl-strict -Wno-undefined-internal -sycl-std=2017 -fsycl-targets=spir64_x86_64-unknown-unknown-sycldevice,spir64_gen-unknown-unknown-sycldevice,spir64_fpga-unknown-unknown-sycldevice,spir64-unknown-unknown-sycldevice /home/user/sycl_workspace/llvm/libdevice/complex_wrapper_fp64.cpp -o /home/user/sycl_workspace/llvm/build/lib/libsycl-complex-fp64.o
error: unable to create target: 'No available targets are compatible with triple "aarch64-unknown-linux-gnu"'
1 error generated.
[4/649] Generating ../../lib/libsycl-cmath.o
FAILED: lib/libsycl-cmath.o
cd /home/user/sycl_workspace/llvm/build/tools/libdevice && /home/user/sycl_workspace/llvm/build/bin/clang-13 -fsycl -c -Wno-sycl-strict -Wno-undefined-internal -sycl-std=2017 -fsycl-targets=spir64_x86_64-unknown-unknown-sycldevice,spir64_gen-unknown-unknown-sycldevice,spir64_fpga-unknown-unknown-sycldevice,spir64-unknown-unknown-sycldevice /home/user/sycl_workspace/llvm/libdevice/cmath_wrapper.cpp -o /home/user/sycl_workspace/llvm/build/lib/libsycl-cmath.o
error: unable to create target: 'No available targets are compatible with triple "aarch64-unknown-linux-gnu"'
1 error generated.
```

**Environment (please complete the following information):**

- OS: Ubuntu 18.04 aarch64
- Target device and vendor: Jetson TX2 (CUDA)
- DPC++ version: commit 78a0b199e1f334938da9d7d1fabcf94937571482
- Dependencies version: N/A

**Additional context**

HipSYCL does build on this target using CUDA, but is missing functionality.