Revert r241620 and follow-up commits while investigating linux buildbot failures.

llvm-svn: 241642
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 3ba1383..3de1159 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -3976,7 +3976,8 @@
 
   // Initialize the stream
   llvm::BitstreamReader StreamFile;
-  PCHContainerOps.ExtractPCH((*Buffer)->getMemBufferRef(), StreamFile);
+  StreamFile.init((const unsigned char *)(*Buffer)->getBufferStart(),
+                  (const unsigned char *)(*Buffer)->getBufferEnd());
   BitstreamCursor Stream(StreamFile);
 
   // Sniff for the signature.