{forceLlvmCodegenBackend,ghcWithPackages}: update clang -fllvm logic

- The LLVM backend always needs an LLVM specific assembler, i.e. clang
  that ideally matches the version of LLVM actually used for codegen.

- The LLVM backend on Darwin requires some version of clang to be
  available. In light of LLVMAS, using a matching version seems to be
  best though this does risk messing with clang used for compiling C
  in the derivation.

  This mess can be avoided by compiling GHC with useLLVM = true which
  sets absolute paths in GHC's settings file. Due to closure size
  constraints, we can't really do that if NCG is available.

pkgs/development/haskell-modules/make-package-set.nix

@@ -734,6 +734,13 @@ package-set { inherit pkgs lib callPackage; } self
   */
   forceLlvmCodegenBackend = overrideCabal (drv: {
     configureFlags = drv.configureFlags or [ ] ++ [ "--ghc-option=-fllvm" ];
-    buildTools = drv.buildTools or [ ] ++ [ self.ghc.llvmPackages.llvm ];
+    buildTools =
+      drv.buildTools or [ ]
+      ++ [ self.ghc.llvmPackages.llvm ]
+      # GHC >= 9.10 needs LLVM specific assembler, i.e. clang
+      # On Darwin clang is always required
+      ++ lib.optionals (lib.versionAtLeast self.ghc.version "9.10" || stdenv.hostPlatform.isDarwin) [
+        self.ghc.llvmPackages.clang
+      ];
   });
 }

pkgs/development/haskell-modules/with-packages-wrapper.nix

@@ -68,10 +68,14 @@ let
     )
   );
   hasLibraries = lib.any (x: x.isHaskellLibrary) paths;
-  # CLang is needed on Darwin for -fllvm to work:
+  # Clang is needed on Darwin for -fllvm to work.
+  # GHC >= 9.10 needs an LLVM specific assembler which we use clang for.
   # https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/codegens.html#llvm-code-generator-fllvm
   llvm = lib.makeBinPath (
-    [ ghc.llvmPackages.llvm ] ++ lib.optional stdenv.targetPlatform.isDarwin ghc.llvmPackages.clang
+    [ ghc.llvmPackages.llvm ]
+    ++ lib.optionals (lib.versionAtLeast ghc.version "9.10" || stdenv.targetPlatform.isDarwin) [
+      ghc.llvmPackages.clang
+    ]
   );
 in