Revert r119838 "Don't warn for empty 'if' body if there is a macro that expands to nothing"
and use a better and more general approach, where NullStmt has a flag to indicate whether it was preceded by an empty macro.

Thanks to Abramo Bagnara for the hint!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@119887 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/TreeTransform.h b/lib/Sema/TreeTransform.h
index 3ae4e5c..807346c 100644
--- a/lib/Sema/TreeTransform.h
+++ b/lib/Sema/TreeTransform.h
@@ -772,11 +772,9 @@
   /// By default, performs semantic analysis to build the new statement.
   /// Subclasses may override this routine to provide different behavior.
   StmtResult RebuildIfStmt(SourceLocation IfLoc, Sema::FullExprArg Cond,
-                                 VarDecl *CondVar, Stmt *Then,
-                                 bool MacroExpandedInThenStmt,
+                                 VarDecl *CondVar, Stmt *Then, 
                                  SourceLocation ElseLoc, Stmt *Else) {
-    return getSema().ActOnIfStmt(IfLoc, Cond, CondVar, Then,
-                                 MacroExpandedInThenStmt, ElseLoc, Else);
+    return getSema().ActOnIfStmt(IfLoc, Cond, CondVar, Then, ElseLoc, Else);
   }
 
   /// \brief Start building a new switch statement.
@@ -3694,7 +3692,7 @@
     return SemaRef.Owned(S);
 
   return getDerived().RebuildIfStmt(S->getIfLoc(), FullCond, ConditionVar,
-                                    Then.get(), S->hasMacroExpandedInThenStmt(),
+                                    Then.get(),
                                     S->getElseLoc(), Else.get());
 }