[Clang][ASan] Correct AsanDtorKindToString to return non-void in default case

[cryptoad]

Summary

Post D96572, a warning started showing up for me:
clang/lib/Basic/Sanitizers.cpp:73:1: warning: control reaches end of non-void function [-Wreturn-type]

So this adds a default to the case to return invalid, which seems appropriate,
and appears to correct the issue.

[cryptoad]

Opt for a version that satisfies clang-diagnostic-covered-switch-default

[delcypher]

@cryptoad Thanks.

LGTM

Originally this code had a default case in the switch but clang complained about it being unnecessary because it was exhaustive, so I removed it... It seems this is causing problems with your compiler :(

clang/lib/Basic/Sanitizers.cpp

StringRef AsanDtorKindToString(llvm::AsanDtorKind kind) {
   switch (kind) {
   case llvm::AsanDtorKind::None:
     return "none";
   case llvm::AsanDtorKind::Global:
     return "global";
   case llvm::AsanDtorKind::Invalid:
     return "invalid";
   }
+  return "invalid";
 }
 
 llvm::AsanDtorKind AsanDtorKindFromString(StringRef kindStr) {
   return llvm::StringSwitch<llvm::AsanDtorKind>(kindStr)
       .Case("none", llvm::AsanDtorKind::None)
       .Case("global", llvm::AsanDtorKind::Global)
       .Default(llvm::AsanDtorKind::Invalid);
 }
 
 } // namespace clang