Ignore modopts/modreqs for UnsafeAccessor field targets

The generated IL remains correct and doesn't
require a .volatile prefix for the generated accessor.
This is based off of what Roslyn currently emits if a
getter was available.

src/coreclr/vm/prestub.cpp

@@ -1497,7 +1497,7 @@ namespace
 
             TokenPairList list { nullptr };
             MetaSig::CompareState state{ &list };
-            state.IgnoreCustomModifiers = false;
+            state.IgnoreCustomModifiers = true;
             if (!DoesFieldMatchUnsafeAccessorDeclaration(cxt, pField, state))
                 continue;
 

src/tests/baseservices/compilerservices/UnsafeAccessors/UnsafeAccessorsTests.cs

@@ -328,6 +328,30 @@ public static void Verify_AccessAllFields_CorElementType()
         extern static ref delegate*<void> GetFPtr(ref AllFields f);
     }
 
+    // Contains fields that have modopts/modreqs
+    struct FieldsWithModifiers
+    {
+        private static volatile int s_vInt;
+        private volatile int _vInt;
+    }
+
+    [Fact]
+    public static void Verify_AccessFieldsWithModifiers()
+    {
+        Console.WriteLine($"Running {nameof(Verify_AccessFieldsWithModifiers)}");
+
+        FieldsWithModifiers fieldsWithModifiers = default;
+
+        GetStaticVolatileInt(ref fieldsWithModifiers) = default;
+        GetVolatileInt(ref fieldsWithModifiers) = default;
+
+        [UnsafeAccessor(UnsafeAccessorKind.StaticField, Name="s_vInt")]
+        extern static ref int GetStaticVolatileInt(ref FieldsWithModifiers f);
+
+        [UnsafeAccessor(UnsafeAccessorKind.Field, Name="_vInt")]
+        extern static ref int GetVolatileInt(ref FieldsWithModifiers f);
+    }
+
     [Fact]
     public static void Verify_AccessStaticMethodClass()
     {