clc: fix DiagnosticOptions related build failure with llvm-21

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/13257
Cc: mesa-stable
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35399>

src/compiler/clc/clc_helpers.cpp

@@ -804,11 +804,17 @@ clc_compile_to_llvm_module(LLVMContext &llvm_ctx,
       c->addDependencyCollector(dep);
    }
 
+#if LLVM_VERSION_MAJOR >= 21
+   auto diag_opts = c->getDiagnosticOpts();
+#else
+   auto diag_opts = &c->getDiagnosticOpts();
+#endif
+
    clang::DiagnosticsEngine diag {
       new clang::DiagnosticIDs,
-      new clang::DiagnosticOptions,
+      diag_opts,
       new clang::TextDiagnosticPrinter(diag_log_stream,
-                                       &c->getDiagnosticOpts())
+                                       diag_opts)
    };
 
 #if LLVM_VERSION_MAJOR >= 17
@@ -865,7 +871,7 @@ clc_compile_to_llvm_module(LLVMContext &llvm_ctx,
 #endif
                    new clang::TextDiagnosticPrinter(
                            diag_log_stream,
-                           &c->getDiagnosticOpts()));
+                           diag_opts));
 
    c->setTarget(clang::TargetInfo::CreateTargetInfo(
 #if LLVM_VERSION_MAJOR >= 21