Help: Do not recommend WCDH in cmake-compile-features(7)

Since commit da7ad799 (WriteCompilerDetectionHeader: Add policy to
remove module, 2020-12-04, v3.20.0-rc1~350^2), the WCDH module is
deprecated.  Update the `cmake-compile-features(7)` manual section that
previously recommended WCDH to make such detection the project's
responsibility instead.  Move the old content of the section over to the
WCDH module to preserve it.
43 jobs for !6037 with doc-compile-features-wcdh in 8 minutes and 34 seconds (queued for 2 seconds)
latest detached
Status Name Job ID Coverage
  Build
manual build:centos6-x86_64 #5730482
cmake build docker linux manual
passed build:debian10-iwyu #5730479
cmake build docker linux

00:04:26

manual build:fedora33-ninja #5730483
cmake build docker linux linux-3.17 manual
passed build:fedora33-sphinx #5730481
cmake build docker linux linux-3.17

00:04:15

passed build:fedora33-tidy #5730480
cmake build docker linux linux-3.17

00:08:34

manual build:macos-x86_64-makefiles #5730485
cmake macos shell xcode-12.4 nonconcurrent manual
manual build:macos-x86_64-ninja #5730484
cmake macos shell xcode-12.4 nonconcurrent manual
manual build:windows-vs2019-x64-ninja #5730486
cmake windows shell vs2019 msvc-19.28-16.9 nonconcurrent manual
 
  Test
created test:fedora33-ninja #5730487
cmake docker linux linux-3.17 x11
created test:macos-x86_64-makefiles #5730489
cmake macos shell xcode-12.4 nonconcurrent
created test:macos-x86_64-ninja #5730488
cmake macos shell xcode-12.4 nonconcurrent
created test:windows-vs2019-x64-ninja #5730490
cmake windows shell vs2019 msvc-19.28-16.9 nonconcurrent
 
  Test Ext
created test:cuda10.2-nvidia #5730493
cmake cuda-rt docker linux
created test:debian10-ninja #5730491
cmake build docker linux linux-3.17
created test:fedora33-makefiles #5730492
docker linux linux-3.17 cmake build
created test:fedora33-ninja-multi #5730494
cmake build docker linux linux-3.17
created test:macos-x86_64-xcode #5730495
cmake macos shell xcode-12.4 concurrent
created test:windows-vs2019-x64 #5730496
cmake windows shell vs2019 msvc-19.28-16.9 concurrent
 
  External
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