[clang][NFC] Annotate SemaStmt.cpp with preferred_type

This helps debuggers to display values in bit-fields in a more helpful way.

clang/lib/Sema/SemaStmt.cpp

@@ -4381,6 +4381,7 @@ Sema::ActOnObjCAutoreleasePoolStmt(SourceLocation AtLoc, Stmt *Body) {
 namespace {
 class CatchHandlerType {
   QualType QT;
+  LLVM_PREFERRED_TYPE(bool)
   unsigned IsPointer : 1;
 
   // This is a special constructor to be used only with DenseMapInfo's