Provide "--ccache" flag for build.sh

[wphicks]

Provide flag to enable ccache for building C, C++, and CUDA code

[dantegd]

Great addition! Just had a couple of requests

[codecov-io]

Codecov Report

Merging #3566 (169af73) into branch-0.19 (6dfff66) will decrease coverage by 6.12%.
The diff coverage is 94.87%.

@@               Coverage Diff               @@
##           branch-0.19    #3566      +/-   ##
===============================================
- Coverage        79.21%   73.09%   -6.13%     
===============================================
  Files              226      214      -12     
  Lines            17900    16977     -923     
===============================================
- Hits             14180    12409    -1771     
- Misses            3720     4568     +848     

Flag	Coverage Δ
dask	?
non-dask	73.09% <94.87%> (+1.61%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
python/cuml/dask/cluster/dbscan.py	48.64% <ø> (-48.58%)	⬇️
python/cuml/dask/linear_model/elastic_net.py	37.50% <ø> (-62.50%)	⬇️
python/cuml/datasets/arima.pyx	97.56% <ø> (ø)
python/cuml/datasets/blobs.py	74.24% <ø> (-3.04%)	⬇️
python/cuml/datasets/regression.pyx	98.11% <ø> (ø)
python/cuml/decomposition/incremental_pca.py	94.70% <ø> (ø)
python/cuml/feature_extraction/_tfidf.py	94.73% <ø> (+0.11%)	⬆️
python/cuml/metrics/pairwise_distances.pyx	98.83% <ø> (ø)
python/cuml/neighbors/__init__.py	100.00% <ø> (ø)
python/cuml/preprocessing/LabelEncoder.py	92.98% <ø> (-1.76%)	⬇️
... and 127 more

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[dantegd]

@gpucibot merge