[lldb] Fix undefined behavior: left shift of negative value

[JDevlieghere]

Summary

Fix undefined behavior in AppleObjCRuntimeV2 where we were left shifting a signed value.

rdar://91242879

[shafik]

Note, in C++20 this was made well-defined see godbolt the paper that did this was P0907R4 Signed Integers are Two’s Complement

[jasonmolenda]

LGTM but unobfuscated is a uint64_t, does this cast do anything now?

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp

if (!actual_class_descriptor_sp) {
       }
     }
     if (!actual_class_descriptor_sp)
       return ObjCLanguageRuntime::ClassDescriptorSP();
     m_cache[slot] = actual_class_descriptor_sp;
   }
 
   uint64_t data_payload =
-      (((uint64_t)unobfuscated << m_objc_debug_taggedpointer_payload_lshift) >>
+      ((unobfuscated << m_objc_debug_taggedpointer_payload_lshift) >>
        m_objc_debug_taggedpointer_payload_rshift);
   int64_t data_payload_signed =
-      ((int64_t)((int64_t)unobfuscated
-                 << m_objc_debug_taggedpointer_payload_lshift) >>
+      ((int64_t)(unobfuscated << m_objc_debug_taggedpointer_payload_lshift) >>
        m_objc_debug_taggedpointer_payload_rshift);
   return ClassDescriptorSP(new ClassDescriptorV2Tagged(
       actual_class_descriptor_sp, data_payload, data_payload_signed));
 }
 
 AppleObjCRuntimeV2::TaggedPointerVendorExtended::TaggedPointerVendorExtended(
     AppleObjCRuntimeV2 &runtime, uint64_t objc_debug_taggedpointer_mask,
     uint64_t objc_debug_taggedpointer_ext_mask,