cmake 3.20: "file does not recognize sub-command COPY_FILE"

[bneradt]

We have agreed to support cmake 3.20 for our cmake builds. I'm getting ready to create a CI job to build with cmake 3.20 and I tested a build with this in rockylinux:8. I observed this cmake failure while running --install:

https://ci.trafficserver.apache.org/job/Github_Builds/job/rocky/2979/console

+ cmake --install cmake-build-quiche
-- Install configuration: "Debug"
-- Installing: /tmp/ats_quiche/lib64/libfastlz.so
...
-- Set runtime path of "/tmp/ats_quiche/libexec/trafficserver/healthchecks.so" to "/tmp/ats_quiche/lib"
-- Installing config: /tmp/ats_quiche/etc/trafficserver/records.yaml
CMake Error at cmake/install_configs.cmake:33 (file):
  file does not recognize sub-command COPY_FILE
Call Stack (most recent call first):
  cmake-build-quiche/configs/cmake_install.cmake:54 (include)
  cmake-build-quiche/cmake_install.cmake:132 (include)

In the meantime, I'll revert PR CI Rocky jobs to use automake.

Reproduction steps:

docker pull ci.trafficserver.apache.org/ats/rockylinux:8
docker run --rm -it ci.trafficserver.apache.org/ats/rockylinux:8 /bin/bash

# Now, from inside docker.
source /opt/rh/gcc-toolset-11/enable

cd /var/tmp
git clone https://github.com/apache/trafficserver.git
cd trafficserver

cmake -B cmake-build-quiche -DCMAKE_COMPILE_WARNING_AS_ERROR=ON -DENABLE_QUICHE=ON -DCMAKE_BUILD_TYPE=Debug -DBUILD_EXPERIMENTAL_PLUGINS=ON -Dquiche_ROOT=/opt/quiche -DOPENSSL_ROOT_DIR=/opt/boringssl -DCMAKE_INSTALL_PREFIX=/tmp/ats_quiche
cmake --build cmake-build-quiche -j4 -v
cmake --install cmake-build-quiche