FindCUDAToolkit: Robust version checks when CUDA lang is not enabled

Previously if you set `CMAKE_CUDA_COMPILER` but hadn't enabled
the CUDA language, FindCUDAToolkit would not correctly compute
the version information.
32 jobs for !5787 with findcudatoolkit_handle_cuda_compiler_without_enabled_lang in 11 minutes and 29 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Build
passed #5525610
linux docker build cmake manual
build:centos6-x86_64

00:07:43

passed #5525607
linux docker build cmake
build:debian10-iwyu

00:01:37

passed #5525611
linux-3.17 linux docker build cmake manual
build:fedora33-ninja

00:01:59

passed #5525609
linux-3.17 linux docker build cmake
build:fedora33-sphinx

00:02:51

passed #5525608
linux-3.17 linux docker build cmake
build:fedora33-tidy

00:03:09

manual #5525613
nonconcurrent xcode-12.3 shell macos cmake manual
build:macos-makefiles
manual #5525612
nonconcurrent xcode-12.3 shell macos cmake manual
build:macos-ninja
manual #5525614
nonconcurrent msvc-19.28 vs2019 shell windows cmake manual
build:windows-vs2019-x64-ninja
 
  Test
passed #5525615
x11 linux-3.17 linux docker cmake
test:fedora33-ninja

00:04:42

created #5525617
nonconcurrent xcode-12.3 shell macos cmake
test:macos-makefiles
created #5525616
nonconcurrent xcode-12.3 shell macos cmake
test:macos-ninja
created #5525618
nonconcurrent msvc-19.28 vs2019 shell windows cmake
test:windows-vs2019-x64-ninja
 
  Test Ext
passed #5525621
linux docker cuda-rt cmake
test:cuda10.2-nvidia

00:00:54

passed #5525619
linux-3.17 linux docker build cmake
test:debian10-ninja

00:02:12

passed #5525620
linux-3.17 linux docker build cmake
test:fedora33-makefiles

00:02:59

passed #5525622
linux-3.17 linux docker build cmake
test:fedora33-ninja-multi

00:02:12

created #5525623
concurrent xcode-12.3 shell macos cmake
test:macos-xcode
created #5525624
concurrent msvc-19.28 vs2019 shell windows cmake
test:windows-vs2019-x64
 
  External
passed cdash

passed ghostflow-check-master

passed ghostflow-stager

passed cdash

passed cdash

passed cdash

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager