Defensively handle fast class generation failure for individual methods

Includes rethrowing of last actual defineClass exception encountered.

Closes gh-27490

spring-core/src/main/java/org/springframework/cglib/core/ReflectUtils.java

@@ -499,6 +499,7 @@ public class ReflectUtils {
 			ProtectionDomain protectionDomain, Class<?> contextClass) throws Exception {
 
 		Class c = null;
+		Throwable t = THROWABLE;
 
 		// Preferred option: JDK 9+ Lookup.defineClass API if ClassLoader matches
 		if (contextClass != null && contextClass.getClassLoader() == loader &&
@@ -516,6 +517,7 @@ public class ReflectUtils {
 				// in case of plain LinkageError (class already defined)
 				// or IllegalArgumentException (class in different package):
 				// fall through to traditional ClassLoader.defineClass below
+				t = target;
 			}
 			catch (Throwable ex) {
 				throw new CodeGenerationException(ex);
@@ -543,6 +545,7 @@ public class ReflectUtils {
 				if (!ex.getClass().getName().endsWith("InaccessibleObjectException")) {
 					throw new CodeGenerationException(ex);
 				}
+				t = ex;
 			}
 		}
 
@@ -564,7 +567,7 @@ public class ReflectUtils {
 
 		// No defineClass variant available at all?
 		if (c == null) {
-			throw new CodeGenerationException(THROWABLE);
+			throw new CodeGenerationException(t);
 		}
 
 		// Force static initializers to run.