[BUG] -Werror causes FAISS build to fail

[zbjornson]

Describe the bug
Since #4075, at least one warning causes a from-source build to fail.

/home/zbbjornson/cuml/cpp/build/_deps/faiss-src/faiss/gpu/impl/DistanceUtils.cuh:291:27: error: comparison of integer expressions of different signedness: ‘unsigned int’ and ‘int’ [-Werror=sign-compare]
  291 |     FAISS_ASSERT(grid.x * k == indices.getSize(1));
      |           ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

This also prevents cuML from building with CUDA 11.5 because some pragmas gained an nv_ prefix.

I'm surprised no one else has hit this yet. Is FAISS built separately and provided through Conda in RAPIDS's CI? I'd consider using -Werror only on cuML code and not on dependencies. https://stackoverflow.com/questions/62932366/compiling-library-with-different-flags-than-main-code shows how to do that.

Steps/Code to reproduce bug
Build from source without using Conda.

Expected behavior
Should build.

Environment details (please complete the following information):

• Environment location: bare metal
• Linux Distro/Architecture: Ubuntu 20.04.1
• GPU Model/Driver: V100, 495.29.05
• CUDA: 11.4
• Method of cuDF & cuML install: from source (cmake 3.21.3, GCC 9.3.0) at 42303fb

[github-actions]

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[github-actions]

This issue has been labeled inactive-90d due to no recent activity in the past 90 days. Please close this issue if no further response or action is needed. Otherwise, please respond with a comment indicating any updates or changes to the original issue and/or confirm this issue still needs to be addressed.