[Lex] Allow to consume tokens while preprocessing

Summary:
By adding a hook to consume all tokens produced by the preprocessor.
The intention of this change is to make it possible to consume the
expanded tokens without re-runnig the preprocessor with minimal changes
to the preprocessor and minimal performance penalty when preprocessing
without recording the tokens.

The added hook is very low-level and reconstructing the expanded token
stream requires more work in the client code, the actual algorithm to
collect the tokens using this hook can be found in the follow-up change.

Reviewers: rsmith

Reviewed By: rsmith

Subscribers: eraman, nemanjai, kbarton, jsji, riccibruno, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D59885

llvm-svn: 361007
diff --git a/clang/lib/Parse/ParseStmtAsm.cpp b/clang/lib/Parse/ParseStmtAsm.cpp
index 3c4bc07..c63808a 100644
--- a/clang/lib/Parse/ParseStmtAsm.cpp
+++ b/clang/lib/Parse/ParseStmtAsm.cpp
@@ -213,7 +213,8 @@
   // Also copy the current token over.
   LineToks.push_back(Tok);
 
-  PP.EnterTokenStream(LineToks, /*DisableMacroExpansions*/ true);
+  PP.EnterTokenStream(LineToks, /*DisableMacroExpansions*/ true,
+                      /*IsReinject*/ true);
 
   // Clear the current token and advance to the first token in LineToks.
   ConsumeAnyToken();