LLVM

"Clang supports a wide variety of C standard library implementations."

https://bcain-llvm.readthedocs.io/projects/clang/en/latest/Toolchain/#c-standard-library

https://releases.llvm.org/12.0.0/docs/Proposals/LLVMLibC.html

https://lpc.events/event/4/contributions/521/attachments/355/586/LPC-2019-toolchains-ClangBuiltLinux.pdf

https://notes.eatonphil.com/compiler-basics-llvm-system-calls.html