Create and promote library aliases in libcudf installations

[trxcllnt]

This PR ensures all cudf::* library aliases are created and promoted to IMPORTED_GLOBAL when find_package(cudf) finds cudf in a local build directory.

This PR shouldn't affect CI or the targets you'd see when libcudf is installed (e.g. by conda), only local source builds.

edit: This now fixes cudf::* alias targets for the libcudf installations too, needed by rapidsai/cuspatial#365.

Validation method:

$ docker run --rm -it \
  -w /tmp/findpackagecudf \
  -v "/tmp/findpackagecudf:/tmp/findpackagecudf" \
  gpuci/miniconda-cuda:10.2-devel-ubuntu18.04 bash

# Set up mamba environment
conda install -y -n base -c conda-forge mamba
mamba update -y -n base -c defaults conda && mamba update -y -n base -c conda-forge mamba
mamba install -y -n base -c conda-forge -c rapidsai-nightly \
    git gtest gmock ninja cmake=3.18 gdal=3.0.2 boost-cpp=1.72.0 cudatoolkit=10.2 libcudf=0.19

# Copy changes in this PR (from the host) to container's /opt/conda/lib/cmake/cudf
# cmake --install $CUDF_ROOT --prefix $CUDF_ROOT/local-install
# docker cp $CUDF_ROOT/local-install/lib/cmake/cudf frosty_agnesi:/opt/conda/lib/cmake/

# Clone cuspatial
git clone https://github.com/trxcllnt/cuspatial.git && cd cuspatial && git checkout fix/cmake-exports

# Configure cuspatial
rm -rf cpp/build && mkdir -p cpp/build \
 && cmake -GNinja -B cpp/build -S cpp \
    -DBUILD_TESTS=ON -DBUILD_BENCHMARKS=ON -DCMAKE_CUDA_ARCHITECTURES=

[codecov]

Codecov Report

Merging #7734 (285f3c3) into branch-0.19 (7871e7a) will increase coverage by 0.65%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           branch-0.19    #7734      +/-   ##
===============================================
+ Coverage        81.86%   82.52%   +0.65%     
===============================================
  Files              101      101              
  Lines            16884    17458     +574     
===============================================
+ Hits             13822    14407     +585     
+ Misses            3062     3051      -11     

Impacted Files	Coverage Δ
python/cudf/cudf/utils/gpu_utils.py	53.65% <0.00%> (-4.88%)	⬇️
python/cudf/cudf/core/column/lists.py	87.68% <0.00%> (-3.72%)	⬇️
python/cudf/cudf/core/column/decimal.py	92.95% <0.00%> (-1.92%)	⬇️
python/cudf/cudf/core/abc.py	87.23% <0.00%> (-1.14%)	⬇️
python/cudf/cudf/core/column/numerical.py	94.83% <0.00%> (-0.20%)	⬇️
python/cudf/cudf/core/column/column.py	87.61% <0.00%> (-0.15%)	⬇️
python/cudf/cudf/utils/utils.py	85.36% <0.00%> (-0.07%)	⬇️
python/cudf/cudf/io/feather.py	100.00% <0.00%> (ø)
python/cudf/cudf/utils/ioutils.py	78.71% <0.00%> (ø)
python/cudf/cudf/comm/serialize.py	0.00% <0.00%> (ø)
... and 45 more

---

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[kkraus14]

Given these are only required if someone uses cudftestutil, how would we feel about not including these and if someone uses cudftestutil they're required to have gtest / gmock installed in their environment?

[trxcllnt]

That's fine with me, just means we have to install them into the gpuCI containers and block merging until the next nightly release.

[trxcllnt]

this change was in reference to rapidsai/cuspatial#365 (comment)

[kkraus14]

They should already be in the gpuci build environment: https://github.com/rapidsai/integration/blob/branch-0.19/conda/recipes/rapids-build-env/meta.yaml#L78-L80

[mike-wendt]

Have we had a run on gpuCI where these didn't work? We install the rapids-build-env in all gpuCI images that we build with so both gtest/gmock should be there

[trxcllnt]

This cuSpatial build failed because CMake couldn't find GTest:

cudf could not be found because dependency GTest could not be found.

But the real reason could due to cuDF not having the changes in this PR. I'll remove these here and in cuSpatial and see what happens.

[kkraus14]

@gpucibot merge