message: add cmake option to define gcc binary to use for host part of CUDA in case there are multiple GCC versions
diff: # Module
  set(MODULE AliHLTTPCCAGPU)
  +option(HLT_CUDA_GCCBIN "GCC binary to use for compiling host part of CUDA code for systems with multiple GCC versions installed" OFF)
  +
  find_package(CUDA)
  if(NOT CUDA_FOUND)
  message( FATAL_ERROR "NVIDIA CUDA package not found. Please install or set HLT_CUDA=OFF" )
  @@ -30,7 +32,10 @@ if(LIBCUDA_SO_PATH_NOTFOUND GREATER -1)
  endif(LIBCUDA_SO_PATH_NOTFOUND GREATER -1)
  #set nvcc flags
  -set(CUDA_NVCC_FLAGS -Wno-deprecated-gpu-targets --use_fast_math --maxrregcount 64 -O4 -Xcompiler -fPIC -Xptxas -O4 -gencode arch=compute_30,code=sm_30 -gencode arch=compute_35,code=sm_35 -gencode arch=compute_52,code=sm_52 -gencode arch=compute_61,code=sm_61 --compiler-bindir /usr/x86_64-pc-linux-gnu/gcc-bin/6.4.0/x86_64-pc-linux-gnu-gcc)
  +set(CUDA_NVCC_FLAGS -Wno-deprecated-gpu-targets --use_fast_math --maxrregcount 64 -O4 -Xcompiler -fPIC -Xptxas -O4 -gencode arch=compute_30,code=sm_30 -gencode arch=compute_35,code=sm_35 -gencode arch=compute_52,code=sm_52 -gencode arch=compute_61,code=sm_61)
  +if(HLT_CUDA_GCCBIN)
  + set(CUDA_NVCC_FLAGS ${CUDA_NVCC_FLAGS} --compiler-bindir ${HLT_CUDA_GCCBIN})
  +endif()
  #for convenience
  set(CAGPUDIR ${AliRoot_SOURCE_DIR}/HLT/TPCLib/tracking-ca/cagpu)
  