Hi,
Technically, it is not a build failure. The build works, but the process is aborted due to a test failure. There is something wrong in the source code, which causes the test to not pass. In the best-case scenario, it's a bug that only affects non-x86 platforms, and in the worst-case scenario, it's an error that exists on all platforms, but it is not exploited by the x86 compiler.
I'll try to take a look at the code to see if I can identify the problem, but perhaps we should open an issue with the creator. I've had similar problems in C++ due to headers that change between different compilers. One example that comes to mind is the abs(float) function in C++, which is defined in some compilers and others uses a version for integers instead of floats if you don't include cmath. The code, as in this case, may still compile, but the results will differ.
But those errors are difficult to detect and require debugging the program. That's why I would first
try to have the author do it, indicating that the tests fail on X
architecture, and then act according to their instructions.