[libc-commits] [libc] [libc][math][c23] Add fsub{, l, f128} and remainderf128 C23 math functions (PR #101576)

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overmighty wrote:

`-DLIBC_USE_NEW_HEADER_GEN=OFF` is still an option, so you should still update libc/spec/stdc.td.

https://github.com/llvm/llvm-project/pull/101576