Sync FindCUDA.cmake with upstream cmake repo (pytorch#11880)

Summary:
Upstream PR: https://gitlab.kitware.com/cmake/cmake/merge_requests/2391/diffs
Pull Request resolved: pytorch#11880

Differential Revision: D9989119

Pulled By: soumith

fbshipit-source-id: 66e87367127975a5f1619fe447f74e76f101b503

Author: peterjc123

README.md

@@ -202,7 +202,7 @@ REM The following two lines are needed for Python 2.7, but the support for it is
 set MSSdk=1
 set FORCE_PY27_BUILD=1
 REM As for CUDA 8, VS2015 Update 3 is also required to build PyTorch. Use the following line.
-set "CUDA_HOST_COMPILER=%VS140COMNTOOLS%\..\..\VC\bin\amd64\cl.exe"
+set "CUDAHOSTCXX=%VS140COMNTOOLS%\..\..\VC\bin\amd64\cl.exe"
 
 call "%VS150COMNTOOLS%\vcvarsall.bat" x64 -vcvars_ver=14.11
 python setup.py install

cmake/Modules_CUDA_fix/upstream/FindCUDA.cmake

@@ -105,6 +105,8 @@
 #      the host compiler is constructed with one or more visual studio macros
 #      such as $(VCInstallDir), that expands out to the path when
 #      the command is run from within VS.
+#      If the CUDAHOSTCXX environment variable is set it will
+#      be used as the default.
 #
 #   CUDA_NVCC_FLAGS
 #   CUDA_NVCC_FLAGS_<CONFIG>
@@ -531,8 +533,8 @@ option(CUDA_HOST_COMPILATION_CPP "Generated file extension" ON)
 # Extra user settable flags
 cmake_initialize_per_config_variable(CUDA_NVCC_FLAGS "Semi-colon delimit multiple arguments.")
 
-if(DEFINED ENV{CUDA_HOST_COMPILER})
-  set(CUDA_HOST_COMPILER "$ENV{CUDA_HOST_COMPILER}" CACHE FILEPATH "Host side compiler used by NVCC")
+if(DEFINED ENV{CUDAHOSTCXX})
+  set(CUDA_HOST_COMPILER "$ENV{CUDAHOSTCXX}" CACHE FILEPATH "Host side compiler used by NVCC")
 elseif(CMAKE_GENERATOR MATCHES "Visual Studio")
   set(_CUDA_MSVC_HOST_COMPILER "$(VCInstallDir)Tools/MSVC/$(VCToolsVersion)/bin/Host$(Platform)/$(PlatformTarget)")
   if(MSVC_VERSION LESS 1910)