The following commit introduced a breakage in ROCm/HIP support for Eigen.
5ec4907434 (1958e65719641efe5483abc4ce0b61806270f6f3_525_517)
```
Building HIPCC object test/CMakeFiles/gpu_basic.dir/gpu_basic_generated_gpu_basic.cu.o
In file included from /home/rocm-user/eigen/test/gpu_basic.cu:20:
In file included from /home/rocm-user/eigen/test/main.h:356:
In file included from /home/rocm-user/eigen/Eigen/QR:11:
In file included from /home/rocm-user/eigen/Eigen/Core:222:
/home/rocm-user/eigen/Eigen/src/Core/arch/GPU/PacketMath.h:556:10: error: use of undeclared identifier 'half2half2'; did you mean '__half2half2'?
return half2half2(from);
^~~~~~~~~~
__half2half2
/opt/rocm/hip/include/hip/hcc_detail/hip_fp16.h:547:21: note: '__half2half2' declared here
__half2 __half2half2(__half x)
^
1 error generated when compiling for gfx900.
```
The cause seems to be a copy-paster error, and the fix is trivial
f3d2ea48f5