[GR-41650] Adjust LLVM backend check for legacy classpath builds.

PullRequest: graal/12934

Author: fniephaus

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/SubstrateOptions.java

@@ -39,7 +39,6 @@
 import java.util.List;
 import java.util.function.Predicate;
 
-import com.oracle.svm.core.c.libc.MuslLibC;
 import org.graalvm.collections.EconomicMap;
 import org.graalvm.collections.UnmodifiableEconomicMap;
 import org.graalvm.compiler.api.replacements.Fold;
@@ -55,6 +54,7 @@
 import org.graalvm.nativeimage.Platforms;
 
 import com.oracle.svm.core.c.libc.LibCBase;
+import com.oracle.svm.core.c.libc.MuslLibC;
 import com.oracle.svm.core.deopt.DeoptimizationSupport;
 import com.oracle.svm.core.heap.ReferenceHandler;
 import com.oracle.svm.core.option.APIOption;
@@ -67,6 +67,8 @@
 import com.oracle.svm.core.thread.VMOperationControl;
 import com.oracle.svm.core.util.UserError;
 import com.oracle.svm.core.util.VMError;
+import com.oracle.svm.util.ModuleSupport;
+import com.oracle.svm.util.ReflectionUtil;
 
 import jdk.internal.misc.Unsafe;
 
@@ -530,7 +532,13 @@ public static long getTearDownFailureNanos() {
         @Override
         protected void onValueUpdate(EconomicMap<OptionKey<?>, Object> values, String oldValue, String newValue) {
             if ("llvm".equals(newValue)) {
-                if (ModuleLayer.boot().findModule("org.graalvm.nativeimage.llvm").isEmpty()) {
+                boolean isLLVMBackendMissing;
+                if (ModuleSupport.modulePathBuild) {
+                    isLLVMBackendMissing = ModuleLayer.boot().findModule("org.graalvm.nativeimage.llvm").isEmpty();
+                } else {
+                    isLLVMBackendMissing = ReflectionUtil.lookupClass(true, "com.oracle.svm.core.graal.llvm.LLVMFeature") == null;
+                }
+                if (isLLVMBackendMissing) {
                     throw UserError.abort("Please install the LLVM backend for GraalVM Native Image via `$JAVA_HOME/bin/gu install native-image-llvm-backend`.");
                 }