Add a CastKind enum to CastExpr. Right now it's not used for much but it will be :)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@77650 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/PCHWriterStmt.cpp b/lib/Frontend/PCHWriterStmt.cpp
index 3e4c6f5..775834b 100644
--- a/lib/Frontend/PCHWriterStmt.cpp
+++ b/lib/Frontend/PCHWriterStmt.cpp
@@ -428,6 +428,7 @@
 void PCHStmtWriter::VisitCastExpr(CastExpr *E) {
   VisitExpr(E);
   Writer.WriteSubStmt(E->getSubExpr());
+  Record.push_back(E->getCastKind()); // FIXME: stable encoding
 }
 
 void PCHStmtWriter::VisitBinaryOperator(BinaryOperator *E) {