Convert switch to exhaustive.

This is a hypothetical case because LLDB doesn't turn on any remarks
in the expression evaluator.

Author: adrian-prantl

lldb/source/Plugins/TypeSystem/Swift/SwiftASTContext.cpp

@@ -2760,18 +2760,19 @@ class StoringDiagnosticConsumer : public swift::DiagnosticConsumer {
       bool use_fixits = false;
       llvm::SourceMgr::DiagKind source_mgr_kind;
       switch (info.Kind) {
-      default:
       case swift::DiagnosticKind::Error:
         source_mgr_kind = llvm::SourceMgr::DK_Error;
         use_fixits = true;
         break;
       case swift::DiagnosticKind::Warning:
         source_mgr_kind = llvm::SourceMgr::DK_Warning;
         break;
-
       case swift::DiagnosticKind::Note:
         source_mgr_kind = llvm::SourceMgr::DK_Note;
         break;
+      case swift::DiagnosticKind::Remark:
+        source_mgr_kind = llvm::SourceMgr::DK_Remark;
+        break;
       }
 
       // Swift may insert note diagnostics after an error diagnostic with fixits