Fix some failures

src/coreclr/System.Private.CoreLib/src/System/Reflection/Emit/EnumBuilder.cs

@@ -39,7 +39,7 @@ public override FieldBuilder DefineLiteral(string literalName, object? literalVa
         }
 
         [return: DynamicallyAccessedMembersAttribute(DynamicallyAccessedMemberTypes.All)]
-        public override TypeInfo? CreateTypeInfo()
+        public override TypeInfo CreateTypeInfo()
         {
             return m_typeBuilder.CreateTypeInfo();
         }

src/coreclr/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilder.cs

@@ -1678,8 +1678,8 @@ private EventBuilder DefineEventNoLock(string name, EventAttributes attributes,
         public override TypeInfo CreateTypeInfo()
         {
             TypeInfo? typeInfo = CreateTypeInfoImpl();
-            Debug.Assert(typeInfo != null);
-            return typeInfo;
+            Debug.Assert(m_isHiddenGlobalType || typeInfo != null);
+            return typeInfo!;
         }
 
         [return: DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]

src/libraries/System.Private.CoreLib/src/System/Reflection/Emit/EnumBuilder.cs

@@ -15,11 +15,11 @@ public virtual FieldBuilder UnderlyingField
             => UnderlyingField;
 
         [return: DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
-        public Type? CreateType()
+        public Type CreateType()
             => CreateTypeInfo();
 
         [return: DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
-        public virtual TypeInfo? CreateTypeInfo()
+        public virtual TypeInfo CreateTypeInfo()
             => CreateTypeInfo();
 
         public virtual FieldBuilder DefineLiteral(string literalName, object literalValue)

src/mono/System.Private.CoreLib/src/System/Reflection/Emit/AssemblyBuilder.Mono.cs

@@ -174,9 +174,6 @@ public override int GetHashCode()
     [StructLayout(LayoutKind.Sequential)]
     public partial class AssemblyBuilder
     {
-        private UIntPtr dynamic_assembly; /* GC-tracked */
-        private Module[]? loaded_modules;
-
         [RequiresDynamicCode("Defining a dynamic assembly requires dynamic code.")]
         public static AssemblyBuilder DefineDynamicAssembly(AssemblyName name, AssemblyBuilderAccess access)
         {
@@ -204,15 +201,19 @@ internal sealed partial class RuntimeAssemblyBuilder : AssemblyBuilder
         //
         // AssemblyBuilder inherits from Assembly, but the runtime thinks its layout inherits from RuntimeAssembly
         //
-    #region Sync with RuntimeAssembly.cs and ReflectionAssembly in object-internals.h
+#region Sync with RuntimeAssembly.cs and ReflectionAssembly in object-internals.h
         internal IntPtr _mono_assembly;
 
+#pragma warning disable CS0169, CA1823 // The field 'RuntimeAssemblyBuilder.dynamic_assembly' is never used
+        private UIntPtr dynamic_assembly; /* GC-tracked */
         private RuntimeModuleBuilder[] modules;
         private string? name;
         private CustomAttributeBuilder[]? cattrs;
         private string? version;
         private string? culture;
         private byte[]? public_key_token;
+        private Module[]? loaded_modules;
+#pragma warning restore CS0169, CA1823 // The field 'RuntimeAssemblyBuilder.loaded_modules' is never used
         private uint access;
 #endregion
 
@@ -222,10 +223,10 @@ internal sealed partial class RuntimeAssemblyBuilder : AssemblyBuilder
 
         [MethodImplAttribute(MethodImplOptions.InternalCall)]
         [DynamicDependency("RuntimeResolve", typeof(RuntimeModuleBuilder))]
-        private static extern void basic_init(AssemblyBuilder ab);
+        private static extern void basic_init(RuntimeAssemblyBuilder ab);
 
         [MethodImplAttribute(MethodImplOptions.InternalCall)]
-        private static extern void UpdateNativeCustomAttributes(AssemblyBuilder ab);
+        private static extern void UpdateNativeCustomAttributes(RuntimeAssemblyBuilder ab);
 
         [DynamicDependency(nameof(access))] // Automatically keeps all previous fields too due to StructLayout
         internal RuntimeAssemblyBuilder(AssemblyName n, AssemblyBuilderAccess access)

src/mono/System.Private.CoreLib/src/System/Reflection/Emit/EnumBuilder.Mono.cs

@@ -193,7 +193,9 @@ public override Type UnderlyingSystemType
         }
 
         [return: DynamicallyAccessedMembersAttribute(DynamicallyAccessedMemberTypes.All)]
-        public override TypeInfo? CreateTypeInfo()
+#pragma warning disable CS8764 // Nullability of return type doesn't match overridden member
+        public override TypeInfo CreateTypeInfo()
+#pragma warning restore CS8764
         {
             return _tb.CreateTypeInfo();
         }