[lldb] Fix building with latest libc++

[mstorsjo]

Summary

Since https://reviews.llvm.org/D157058 in libc++,
the base template for char_traits has been removed - it is only
provided for char, wchar_t, char8_t, char16_t and char32_t.
(Thus, to use basic_string with a type other than those, we'd need
to supply suitable traits ourselves.)

For this particular use, a vector works just as well as basic_string.

[DavidSpickett]

LGTM.

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp

static void WriteRegisterValueInHexFixedWidth(
 
   if (reg_value_p) {
     AppendHexValue(response, (const uint8_t *)reg_value_p->GetBytes(),
                    reg_value_p->GetByteSize(),
                    byte_order == lldb::eByteOrderLittle);
   } else {
     // Zero-out any unreadable values.
     if (reg_info.byte_size > 0) {
-      std::basic_string<uint8_t> zeros(reg_info.byte_size, '\0');
+      std::vector<uint8_t> zeros(reg_info.byte_size, '\0');
       AppendHexValue(response, zeros.data(), zeros.size(), false);
     }
   }
 }
 
 static std::optional<json::Object>
 GetRegistersAsJSON(NativeThreadProtocol &thread) {
   Log *log = GetLog(LLDBLog::Thread);