llvmPackages_{12,13,14,15,16,17,git}.libcxx: add LIBCXXABI_COMPILER_RT flag

[ghost]

Description of changes

fix for aarch64-linux pkgLLVM.libcxx
https://hydra.nixos.org/build/253162977

when building pkgsLLVM.stdenv on aarch64-linux the build fails when building libcxxabi due to the undefined symbols

                 U __aarch64_ldadd4_acq_rel
                 U __aarch64_ldadd8_acq_rel
                 U __aarch64_swp8_acq_rel

setting the cmake flag LIBCXXABI_COMPILER_RT=ON adds compiler-rt to the link step. note that for libcxx we already set the flag LIBCXX_COMPILER_RT=ON.

https://clang.llvm.org/docs/Toolchain.html#compiler-rt-llvm

change #292043 merged libcxx and libcxxabi builds and thus libcxxabi is now getting compiled with the -rtlib=compiler-rt flag. This flag uses the clang runtime functions and thus needs to link with the their implementation, which is what LIBCXXABI_COMPILER_RT=ON does. when compiled without -rtlib=compiler-rt on aarch64 it seems that clang just inlines the implementation so no function call is required. When compiler-rt libraries are available the optimizer decides that a function call is preferable to inlining.

testing:

for x in {12..17} git; nix-build -A pkgsCross.aarch64-multiplatform.pkgsLLVM.llvmPackages_$x.libcxx

llvm14 fails building libunwind, which is a per-existing issue.
llvmgit fails while building compiler-rt

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.05 Release Notes (or backporting 23.05 and 23.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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