[lldb] Silence GCC warnings about missing returns after fully covered switches. NFC.

[mstorsjo]

Summary

This silences warnings like this:

lldb/source/Core/DebuggerEvents.cpp: In member function ‘llvm::StringRef lldb_private::DiagnosticEventData::GetPrefix() const’:
lldb/source/Core/DebuggerEvents.cpp:55:1: warning: control reaches end of non-void function [-Wreturn-type]

55 | }

[labath]

Yes, that's the way we usually deal with this.

[JDevlieghere]

Thanks!

lldb/source/Breakpoint/Breakpoint.cpp

switch (type) {
     case eBreakpointEventTypeEnabled: return "breakpoint enabled";
     case eBreakpointEventTypeDisabled: return "breakpoint disabled";
     case eBreakpointEventTypeCommandChanged: return "command changed";
     case eBreakpointEventTypeConditionChanged: return "condition changed";
     case eBreakpointEventTypeIgnoreChanged: return "ignore count changed";
     case eBreakpointEventTypeThreadChanged: return "thread changed";
     case eBreakpointEventTypeAutoContinueChanged: return "autocontinue changed";
   };
+  llvm_unreachable("Fully covered switch above!");
 }
 
 Log *Breakpoint::BreakpointEventData::GetLogChannel() {
   return GetLog(LLDBLog::Breakpoints);
 }
 
 Breakpoint::BreakpointEventData::BreakpointEventData(
     BreakpointEventType sub_type, const BreakpointSP &new_breakpoint_sp)

lldb/source/Core/DebuggerEvents.cpp

 
 llvm::StringRef DiagnosticEventData::GetPrefix() const {
   switch (m_type) {
   case Type::Warning:
     return "warning";
   case Type::Error:
     return "error";
   }
+  llvm_unreachable("Fully covered switch above!");
 }
 
 void DiagnosticEventData::Dump(Stream *s) const {
   *s << GetPrefix() << ": " << GetMessage() << '\n';
   s->Flush();
 }
 
 ConstString DiagnosticEventData::GetFlavorString() {

lldb/source/Plugins/Process/Linux/IntelPTCollector.cpp

auto getRadix = [&]() {
     switch (type) {
     case Hex:
       return 16;
     case ZeroOne:
     case Decimal:
     case BitOffset:
       return 10;
     }
+    llvm_unreachable("Fully covered switch above!");
   };
 
   auto createError = [&](const char *expected_value_message) {
     return createStringError(
         inconvertibleErrorCode(),
         "The file '%s' has an invalid value. It should be %s.", file,
         expected_value_message);
   };