Preprocessor: Clarify the ownership of the IncludeMacroStack with unique_ptr.

llvm-svn: 204007
diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index 2125d18..d85df38 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -143,11 +143,7 @@
 Preprocessor::~Preprocessor() {
   assert(BacktrackPositions.empty() && "EnableBacktrack/Backtrack imbalance!");
 
-  while (!IncludeMacroStack.empty()) {
-    delete IncludeMacroStack.back().TheLexer;
-    delete IncludeMacroStack.back().TheTokenLexer;
-    IncludeMacroStack.pop_back();
-  }
+  IncludeMacroStack.clear();
 
   // Free any macro definitions.
   for (MacroInfoChain *I = MIChainHead ; I ; I = I->Next)