[lldb] Fix compiler error in ValueObject tests

Fixes 0cbc498.

error: non-constant-expression cannot be narrowed from type 'uint64_t' (aka 'unsigned long long') to 'size_t' (aka 'unsigned int') in initializer list [-Wc++11-narrowing]
   71 |                     in_value.GetLocalBufferSize()};
      |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Given this is test code, I think a static cast is fine here.

Tiny risk that it's actually a symptom of a bug that would
happen if you did 32-bit to 64-bit debugging. I expect you'd
find a lot more bugs than that though.

Author: DavidSpickett

lldb/unittests/ValueObject/DynamicValueObjectLocalBuffer.cpp

@@ -68,7 +68,7 @@ struct MockLanguageRuntime : public LanguageRuntime {
     class_type_or_name.SetCompilerType(int_type);
     local_buffer = {(uint8_t *)in_value.GetValue().GetScalar().ULongLong(
                         LLDB_INVALID_ADDRESS),
-                    in_value.GetLocalBufferSize()};
+                    static_cast<size_t>(in_value.GetLocalBufferSize())};
     value_type = Value::ValueType::HostAddress;
 
     return true;