CUDA: improve regex for CUDA Toolkit root from nvcc verbose output

The original regular expression was greedy and would match any
environment variable ending with `TOP` (like `DESKTOP`). This is an
issue on windows where `nvcc -v` would output all environment variables
before the compiler's verbose output.

To resolve this issue we use a tighter match algorithm that looks
for `#$ TOP=` instead of `TOP=`.

Fixes: #22158
34 jobs for !6094 with improve_cuda_toolkit_extraction_regex in 8 minutes and 44 seconds (queued for 3 seconds)
latest detached
Status Name Job ID Coverage
  Build
manual build:centos6-x86_64 #5768029
cmake build docker linux manual
passed build:debian10-iwyu #5768026
cmake build docker linux

00:05:28

manual build:fedora33-ninja #5768030
cmake build docker linux linux-3.17 manual
passed build:fedora33-sphinx #5768028
cmake build docker linux linux-3.17

00:07:59

passed build:fedora33-tidy #5768027
cmake build docker linux linux-3.17

00:08:44

manual build:macos-x86_64-makefiles #5768032
cmake macos shell xcode-12.4 nonconcurrent manual
manual build:macos-x86_64-ninja #5768031
cmake macos shell xcode-12.4 nonconcurrent manual
manual build:windows-vs2019-x64-ninja #5768033
cmake windows shell vs2019 msvc-19.28-16.9 nonconcurrent manual
 
  Test
created test:fedora33-ninja #5768034
cmake docker linux linux-3.17 x11
created test:macos-x86_64-makefiles #5768036
cmake macos shell xcode-12.4 nonconcurrent
created test:macos-x86_64-ninja #5768035
cmake macos shell xcode-12.4 nonconcurrent
created test:windows-vs2019-x64-ninja #5768037
cmake windows shell vs2019 msvc-19.28-16.9 nonconcurrent
 
  Test Ext
created test:cuda10.2-nvidia #5768040
cmake cuda-rt docker linux
created test:debian10-ninja #5768038
linux-3.17 cmake build docker linux
created test:fedora33-makefiles #5768039
cmake build docker linux linux-3.17
created test:fedora33-ninja-multi #5768041
cmake build docker linux linux-3.17
created test:macos-x86_64-xcode #5768042
cmake macos shell xcode-12.4 concurrent
created test:windows-vs2019-x64 #5768043
cmake windows shell vs2019 msvc-19.28-16.9 concurrent
 
  External
passed cdash

passed ghostflow-check-master

passed ghostflow-check-release

passed ghostflow-stager

passed cdash

passed cdash

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