A bit related to JENKINS-64612. The clang-tidy tool reports warnings generated by gcc.

This is a bigger problem than it may seem. You could argue "well, just put them in different files for different tools to parse", but a common way to run clang-tidy is via cmake as 

cmake -DCMAKE_CXX_CLANG_TIDY=clang-tidy .. && cmake --build .

Meaning both the clang-tidy and gcc warnings are generated as a result of the same command being executed. This can't be separated (https://discourse.cmake.org/t/run-clang-tidy-only/2537), and has benefits over other ways of running clang-tidy (only check the files that have changed in incremental builds).

In the same way JENKINS-64612 argues for only including warnings with a "-W" in them, here I would like to argue that the clang-tidy tool should filter-out the warnings with a "-W" in them.

In fact, as of clang-tidy 11.0.0, the only categories clang-tidy reports are:

abseil-*
android-*
boost-*
bugprone-*
cert-*
clang-analyzer-*
cppcoreguidelines-*
darwin-*
fuchsia-*
google-*
hicpp-*
linuxkernel-*
llvm-*
llvmlibc-*
misc-*
modernize-*
mpi-*
objc-*
openmp-*
performance-*
portability-*
readability-*
zircon-*

(none of them starting with "-W").