[clang][Interp][NFC] Add missing fallthrough when parsing While loops

Author: tbaederr

clang/lib/AST/Interp/Compiler.cpp

@@ -4373,6 +4373,7 @@ bool Compiler<Emitter>::visitWhileStmt(const WhileStmt *S) {
 
   if (!this->jump(CondLabel))
     return false;
+  this->fallthrough(EndLabel);
   this->emitLabel(EndLabel);
 
   return true;