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At the moment, due to a bug that needs further investigation, clang is failing to find the builtins, and adding the path to the builtin library as described in the https://clang.llvm.org/docs/UsersManual.html#finding-clang-runtime-libraries doesn’t seem to be working either (bug report pending, since the LLVM bugzilla is currently locked due to the upstream migration to Github issues). However, we can work around this issue by adding the builtin library directly on every link command (-DCMAKE_EXE_LINKER_FLAGS=path/to/clang_rt.builtins-aarch64.lib).
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