Add version number checking to PTH files.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@63047 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/Driver/CacheTokens.cpp b/Driver/CacheTokens.cpp
index 975d364..aef59cb 100644
--- a/Driver/CacheTokens.cpp
+++ b/Driver/CacheTokens.cpp
@@ -456,6 +456,7 @@
 void PTHWriter::GeneratePTH() {
   // Generate the prologue.
   Out << "cfe-pth";
+  Emit32(PTHManager::Version);
   Offset JumpOffset = Out.tell();
   Emit32(0);