[HIPIFY][feature] New hipification strategy: Single source file for CUDA/HIP code

[emankov]

The idea is to introduce yet another hipification approach: instead of a new hipified file or hipification in-place perform hipification in the source CUDA file by keeping both CUDA and HIP code in it.

[Example]

#if GPU_PLATFORM == NVIDIA
  #include <cuda_runtime_api.h>
  #include <cublas_v2.h>
#elif GPU_PLATFORM == AMD
  #include <hip/hip_runtime.h>
  #include <hip/hip_runtime_api.h>
  #include <hipblas.h>
  #define cudaError_t hipError_t
  #define cudaFree hipFree
  #define cudaMalloc hipMalloc
  #define cudaMemcpy hipMemcpy
  #define cublasHandle_t hipblasHandle_t
  #define cublasIdamin hipblasIdamin
  #define cublasStatus_t hipblasStatus_t
#endif

[on deliberation]
For compiling such a single-source hipified code the following defines should be provided:
for AMD: -DNVIDIA=0 -DAMD=1 -DGPU_PLATFORM=AMD
for NVIDIA: -DNVIDIA=0 -DAMD=1 -DGPU_PLATFORM=NVIDIA

[IMP]
Both approaches should be available in hipify-clang first under corresponding options.