cmake: guess location of nvcc if it can't be found (apache#17293)

* [Build] Add a reasonable default for CMAKE_CUDA_COMPILER in *nix

* CR

* CR

* Update as per CR comments

* include(CheckLanguage)

Co-authored-by: Leonard Lausen <leonard@lausen.nl>

CMakeLists.txt

@@ -87,6 +87,12 @@ message(STATUS "CMake version '${CMAKE_VERSION}' using generator '${CMAKE_GENERA
 project(mxnet C CXX)
 if(USE_CUDA)
   cmake_minimum_required(VERSION 3.13.2)  # CUDA 10 (Turing) detection available starting 3.13.2
+  include(CheckLanguage)
+  check_language(CUDA)
+  if (NOT CMAKE_CUDA_COMPILER_LOADED AND UNIX AND EXISTS "/usr/local/cuda/bin/nvcc")
+    set(CMAKE_CUDA_COMPILER "/usr/local/cuda/bin/nvcc")
+    message(WARNING "CMAKE_CUDA_COMPILER guessed: ${CMAKE_CUDA_COMPILER}")
+  endif()
   enable_language(CUDA)
   set(CMAKE_CUDA_STANDARD 11)
   include(CheckCXXCompilerFlag)
@@ -592,7 +598,6 @@ if(USE_CUDA)
 
   string(REPLACE ";" " " CUDA_ARCH_FLAGS_SPACES "${CUDA_ARCH_FLAGS}")
 
-
   find_package(CUDAToolkit REQUIRED cublas cufft cusolver curand
     OPTIONAL_COMPONENTS nvToolsExt nvrtc)