BinUtils: Use more-private temporary variable names

Since commit 4d786dfc (BinUtils: Avoid clobbering a variable named
without a private prefix, 2021-04-06, v3.20.1~4^2) we use variables
named `_tool` and `_name`, but these may still be common enough to
affect project code.  Use `_CMAKE_TOOL` and `_CMAKE_TOOL_NAME` instead,
and unset them when finished.

Fixes: #22140
29 jobs for !6085 with binutils-var-private in 16 minutes and 56 seconds (queued for 4 seconds)
latest detached
Status Name Job ID Coverage
  Build
passed build:centos6-x86_64 #5762587
cmake build docker linux manual

00:04:21

passed build:debian10-iwyu #5762584
cmake build docker linux

00:02:12

passed build:fedora33-ninja #5762588
cmake build docker linux linux-3.17 manual

00:01:09

passed build:fedora33-sphinx #5762586
cmake build docker linux linux-3.17

00:04:38

passed build:fedora33-tidy #5762585
cmake build docker linux linux-3.17

00:09:42

manual build:macos-x86_64-makefiles #5762590
cmake macos shell xcode-12.4 nonconcurrent manual
manual build:macos-x86_64-ninja #5762589
cmake macos shell xcode-12.4 nonconcurrent manual
manual build:windows-vs2019-x64-ninja #5762591
cmake windows shell vs2019 msvc-19.28-16.9 nonconcurrent manual
 
  Test
passed test:fedora33-ninja #5762592
cmake docker linux linux-3.17 x11

00:10:28

created test:macos-x86_64-makefiles #5762594
cmake macos shell xcode-12.4 nonconcurrent
created test:macos-x86_64-ninja #5762593
cmake macos shell xcode-12.4 nonconcurrent
created test:windows-vs2019-x64-ninja #5762595
cmake windows shell vs2019 msvc-19.28-16.9 nonconcurrent
 
  Test Ext
passed test:cuda10.2-nvidia #5762598
cmake cuda-rt docker linux

00:00:51

passed test:debian10-ninja #5762596
cmake build docker linux linux-3.17

00:03:17

passed test:fedora33-makefiles #5762597
build docker linux linux-3.17 cmake

00:11:09

passed test:fedora33-ninja-multi #5762599
cmake build docker linux linux-3.17

00:03:48

created test:macos-x86_64-xcode #5762600
cmake macos shell xcode-12.4 concurrent
created test:windows-vs2019-x64 #5762601
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 ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager