[FEA] Enable building static libs

[trxcllnt]

This PR allows building libcuml++ static libs via CMake option -DBUILD_SHARED_LIBS=ON|OFF.

I was seeing a linker error due to not having -fPIC enabled, but I wouldn't have expected this to affect static libs. I'll investigate some more and turn it off if possible, but for now -fPIC is enabled.

[robertmaynard]

I was seeing a linker error due to not having -fPIC enabled, but I wouldn't have expected this to affect static libs. I'll investigate some more and turn it off if possible, but for now -fPIC is enabled.

All static code that will be embedded in to a shared library needs to be compiled with fPIC. Code that will be embedded into a binary that isn't compiled with fPIE has no such requirement ( statement presumes x86_64 arch ).

[dantegd]

rerun tests

[dantegd]

@gpucibot merge

[trxcllnt]

rerun tests

[trxcllnt]

rerun tests

[trxcllnt]

Not sure what this is about, but this seems unrelated to this PR:

FAILED: CMakeFiles/cuml++.dir/src/randomforest/randomforest.cu.o 
sccache /usr/local/cuda/bin/nvcc -forward-unknown-to-host-compiler -ccbin=/usr/bin/g++ -DCUML_CPP_API -DDISABLE_CUSPARSE_DEPRECATED -DRAFT_DISTANCE_COMPILED -DRAFT_NN_COMPILED -DTHRUST_DEVICE_SYSTEM=THRUST_DEVICE_SYSTEM_CUDA -DTHRUST_HOST_SYSTEM=THRUST_HOST_SYSTEM_CPP -Dcuml___EXPORTS -I$SRC_DIR/cpp/include -I$SRC_DIR/cpp/src -I$SRC_DIR/cpp/src/metrics -I$SRC_DIR/cpp/src_prims -I$PREFIX/include/rapids/thrust -I$PREFIX/include/rapids/thrust/dependencies -I$SRC_DIR/cpp/build/_deps/gputreeshap-src -isystem=$PREFIX/include -isystem=/usr/local/cuda/include -O3 -DNDEBUG --generate-code=arch=compute_60,code=[sm_60] --generate-code=arch=compute_70,code=[sm_70] --generate-code=arch=compute_75,code=[sm_75] --generate-code=arch=compute_80,code=[sm_80] --generate-code=arch=compute_86,code=[compute_86,sm_86] -Xcompiler=-fPIC --expt-extended-lambda --expt-relaxed-constexpr -Werror=all-warnings -Xcompiler=-Wall,-Werror,-Wno-error=deprecated-declarations,-Wno-error=sign-compare -Xcompiler=-Wno-deprecated-declarations -Xfatbin=-compress-all -Xcompiler=-fopenmp -Xcompiler -pthread -std=c++17 -MD -MT CMakeFiles/cuml++.dir/src/randomforest/randomforest.cu.o -MF CMakeFiles/cuml++.dir/src/randomforest/randomforest.cu.o.d -x cu -c $SRC_DIR/cpp/src/randomforest/randomforest.cu -o CMakeFiles/cuml++.dir/src/randomforest/randomforest.cu.o
$PREFIX/include/raft/random/detail/rng_impl.cuh(79): error: expected an identifier

[trxcllnt]

rerun tests

[trxcllnt]

rerun tests

[trxcllnt]

rerun tests

[codecov-commenter]

Codecov Report

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@@               Coverage Diff               @@
##             branch-22.06    #4673   +/-   ##
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  Branches                ?        0           
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  Misses                  ?     2286           
  Partials                ?        0           

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