llvmPackages_15: apply #211230 to llvmPackages_15

See the comments here for context: https://github.com/NixOS/nixpkgs/pull/194634#discussion_r1089389188

Co-authored-by: Weijia Wang <9713184+wegank@users.noreply.github.com>

pkgs/development/compilers/llvm/15/default.nix

@@ -114,7 +114,7 @@ let
       cc = tools.clang-unwrapped;
       libcxx = targetLlvmLibraries.libcxx;
       extraPackages = [
-        targetLlvmLibraries.libcxxabi
+        libcxx.cxxabi
         targetLlvmLibraries.compiler-rt
       ];
       extraBuildCommands = mkExtraBuildCommands cc;
@@ -154,7 +154,7 @@ let
       libcxx = targetLlvmLibraries.libcxx;
       bintools = bintools';
       extraPackages = [
-        targetLlvmLibraries.libcxxabi
+        libcxx.cxxabi
         targetLlvmLibraries.compiler-rt
       ] ++ lib.optionals (!stdenv.targetPlatform.isWasm) [
         targetLlvmLibraries.libunwind
@@ -167,7 +167,7 @@ let
         ]
         ++ lib.optional (!stdenv.targetPlatform.isWasm) "--unwindlib=libunwind"
         ++ lib.optional
-          (!stdenv.targetPlatform.isWasm && !stdenv.targetPlatform.isFreeBSD && stdenv.targetPlatform.useLLVM or false)
+          (!stdenv.targetPlatform.isWasm && stdenv.targetPlatform.useLLVM or false)
           "-lunwind"
         ++ lib.optional stdenv.targetPlatform.isWasm "-fno-exceptions";
     };

pkgs/development/compilers/llvm/15/libcxx/default.nix

@@ -1,7 +1,8 @@
 { lib, stdenv, llvm_meta
 , monorepoSrc, runCommand
 , cmake, python3, fixDarwinDylibNames, version
-, libcxxabi
+, cxxabi ? if stdenv.hostPlatform.isFreeBSD then libcxxrt else libcxxabi
+, libcxxabi, libcxxrt
 , enableShared ? !stdenv.hostPlatform.isStatic
 
 # If headersOnly is true, the resulting package would only include the headers.
@@ -16,6 +17,8 @@ let
   basename = "libcxx";
 in
 
+assert stdenv.isDarwin -> cxxabi.libName == "c++abi";
+
 stdenv.mkDerivation rec {
   pname = basename + lib.optionalString headersOnly "-headers";
   inherit version;
@@ -59,12 +62,18 @@ stdenv.mkDerivation rec {
   nativeBuildInputs = [ cmake python3 ]
     ++ lib.optional stdenv.isDarwin fixDarwinDylibNames;
 
-  buildInputs = lib.optionals (!headersOnly) [ libcxxabi ];
+  buildInputs = lib.optionals (!headersOnly) [ cxxabi ];
 
-  cmakeFlags = [
+  cmakeFlags = let
+    # See: https://libcxx.llvm.org/BuildingLibcxx.html#cmdoption-arg-libcxx-cxx-abi-string
+    libcxx_cxx_abi_opt = {
+      "c++abi" = "system-libcxxabi";
+      "cxxrt" = "libcxxrt";
+    }.${cxxabi.libName} or (throw "unknown cxxabi: ${cxxabi.libName} (${cxxabi.pname})");
+  in [
     "-DLLVM_ENABLE_RUNTIMES=libcxx"
-    "-DLIBCXX_CXX_ABI=${if headersOnly then "none" else "system-libcxxabi"}"
-  ] ++ lib.optional (!headersOnly) "-DLIBCXX_CXX_ABI_INCLUDE_PATHS=${libcxxabi.dev}/include/c++/v1"
+    "-DLIBCXX_CXX_ABI=${if headersOnly then "none" else libcxx_cxx_abi_opt}"
+  ] ++ lib.optional (!headersOnly && cxxabi.libName == "c++abi") "-DLIBCXX_CXX_ABI_INCLUDE_PATHS=${cxxabi.dev}/include/c++/v1"
     ++ lib.optional (stdenv.hostPlatform.isMusl || stdenv.hostPlatform.isWasi) "-DLIBCXX_HAS_MUSL_LIBC=1"
     ++ lib.optional (stdenv.hostPlatform.useLLVM or false) "-DLIBCXX_USE_COMPILER_RT=ON"
     ++ lib.optionals stdenv.hostPlatform.isWasm [
@@ -78,6 +87,7 @@ stdenv.mkDerivation rec {
 
   passthru = {
     isLLVM = true;
+    inherit cxxabi;
   };
 
   meta = llvm_meta // {

pkgs/development/compilers/llvm/15/libcxxabi/default.nix

@@ -83,6 +83,10 @@ stdenv.mkDerivation rec {
     install -m 644 ../../${pname}/include/${if stdenv.isDarwin then "*" else "cxxabi.h"} "$dev/include"
   '';
 
+  passthru = {
+    libName = "c++abi";
+  };
+
   meta = llvm_meta // {
     homepage = "https://libcxxabi.llvm.org/";
     description = "Provides C++ standard library support";