[lldb] Fix warnings

This patch fixes:

  lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp:415:7:
  error: label at end of compound statement is a C++23 extension
  [-Werror,-Wc++23-extensions]

  lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp:536:7:
  error: label at end of compound statement is a C++23 extension
  [-Werror,-Wc++23-extensions]

  lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp:672:7:
  error: label at end of compound statement is a C++23 extension
  [-Werror,-Wc++23-extensions]

Author: kazutakahirata

lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp

@@ -412,6 +412,7 @@ class RegisterContextDarwin_arm_Mach : public RegisterContextDarwin_arm {
         break;
 
       default:
+        break;
       }
       offset = next_thread_state;
     }
@@ -533,6 +534,7 @@ class RegisterContextDarwin_arm64_Mach : public RegisterContextDarwin_arm64 {
         }
         break;
       default:
+        break;
       }
       offset = next_thread_state;
     }
@@ -669,6 +671,7 @@ class RegisterContextDarwin_riscv32_Mach
         }
         break;
       default:
+        break;
       }
       offset = next_thread_state;
     }