[SYCL] [HIP] `__CUDA_ARCH__` defined when compiling for HIP backend

[AuroraPerego]

Describe the bug
I noticed that __CUDA_ARCH__ is defined when compiling ahead of time for the HIP backend.
I don't know if this is wanted, but for example using Eigen I get an error because it tries to include CUDA libraries (the workaround here is to define EIGEN_NO_CUDA).

As an example, compiling a file that just includes the Eigen library gives this:

In file included from include_eigen.cpp:3:
In file included from eigen/Eigen/Core:160:
eigen/Eigen/src/Core/util/Meta.h:21:12: fatal error: 'math_constants.h' file not found
  #include <math_constants.h>
           ^~~~~~~~~~~~~~~~~~

To Reproduce

$ clang++ -fsycl -std=c++17 dummy.cpp -dM -E  -fsycl-targets=amdgcn-amd-amdhsa -Xsycl-target-backend --offload-arch=gfx900 --rocm-path=/opt/rocm-5.0.2 | grep CUDA_ARCH
#define __CUDA_ARCH__ 1

where dummy.cpp is just

#include <CL/sycl.hpp>

int main(){
    return 0;
}

Environment (please complete the following information):

• OS: Linux
• Target device and vendor: AMD GPU Radeon PRO WX 9100
• clang version: 16.0.0 (https://github.com/intel/llvm 0f579ba)
  release 2022-09 (but it tried also with the sycl-nightly/20221208 and the behaviour is the same)