[NFC][clang] Fix static code analyzer complains

[Fznamznon]

Summary

Initialize values that end up uninitialized.

clang/lib/ARCMigrate/TransformActions.cpp

enum ActionKind {
     Act_ClearDiagnostic
   };
 
   struct ActionData {
     ActionKind Kind;
     SourceLocation Loc;
     SourceRange R1, R2;
     StringRef Text1, Text2;
-    Stmt *S;
+    Stmt *S = nullptr;
     SmallVector<unsigned, 2> DiagIDs;
   };
 
   std::vector<ActionData> CachedActions;
 
   enum RangeComparison {
     Range_Before,
     Range_After,

clang/lib/Sema/AnalysisBasedWarnings.cpp

static CheckFallThroughDiagnostics MakeForCoroutine(const Decl *Func) {
     CheckFallThroughDiagnostics D;
     D.FuncLoc = Func->getLocation();
     D.diag_MaybeFallThrough_HasNoReturn = 0;
     D.diag_MaybeFallThrough_ReturnsNonVoid =
         diag::warn_maybe_falloff_nonvoid_coroutine;
     D.diag_AlwaysFallThrough_HasNoReturn = 0;
     D.diag_AlwaysFallThrough_ReturnsNonVoid =
         diag::warn_falloff_nonvoid_coroutine;
+    D.diag_NeverFallThroughOrReturn = 0;
     D.funMode = Coroutine;
     return D;
   }
 
   static CheckFallThroughDiagnostics MakeForBlock() {
     CheckFallThroughDiagnostics D;
     D.diag_MaybeFallThrough_HasNoReturn =
       diag::err_noreturn_block_has_return_expr;