[libc-commits] [clang] [libc] [libcxx] [libc][libcxx] Support for building libc++ against LLVM libc (PR #99287)

[Joseph Huber via libc-commits]

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@@ -293,6 +293,7 @@ option(LIBCXX_ENABLE_THREADS "Build libc++ with support for threads." ON)
 option(LIBCXX_ENABLE_MONOTONIC_CLOCK
   "Build libc++ with support for a monotonic clock.
    This option may only be set to OFF when LIBCXX_ENABLE_THREADS=OFF." ON)
+option(LIBCXX_USE_LLVM_LIBC "Build libc++ against LLVM libc." OFF)
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jhuber6 wrote:

That was my original thought, but I don't think the different C libraries have enough granularity for this to be anything but a binary flag in practice. What this flag truly means is whether or not to use the LLVM `libc` built in-tree or not. It's basically the exact same use-case as the already present `LIBCXXABI_USE_LLVM_UNWINDER`. If someone installed the LLVM libc globally, then the existing logic would just pick it up as the `libc` without this flag.

https://github.com/llvm/llvm-project/pull/99287