[Clang] - Update code to match upcoming llvm::zlib API.

[grimar]

Summary

D28684 changed llvm::zlib to return Error instead of Status.
It was accepted and committed in r292214, but then reverted in r292217
because I missed that clang code also needs to be updated.

Patch do that.

lib/Serialization/ASTReader.cpp

 #include "llvm/ADT/APSInt.h"
 #include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/Bitcode/BitstreamReader.h"
 #include "llvm/Support/Compression.h"
 #include "llvm/Support/Compiler.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/SaveAndRestore.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <cassert>
auto ReadBuffer = [this](
       BitstreamCursor &SLocEntryCursor,
       StringRef Name) -> std::unique_ptr<llvm::MemoryBuffer> {
     RecordData Record;
     StringRef Blob;
     unsigned Code = SLocEntryCursor.ReadCode();
     unsigned RecCode = SLocEntryCursor.readRecord(Code, Record, &Blob);
 
     if (RecCode == SM_SLOC_BUFFER_BLOB_COMPRESSED) {
+      if (!llvm::zlib::isAvailable()) {
+        Error("zlib is not available");
+        return nullptr;
+      }
       SmallString<0> Uncompressed;
-      if (llvm::zlib::uncompress(Blob, Uncompressed, Record[0]) !=
-          llvm::zlib::StatusOK) {
-        Error("could not decompress embedded file contents");
+      if (llvm::Error E =
+              llvm::zlib::uncompress(Blob, Uncompressed, Record[0])) {
+        Error("could not decompress embedded file contents: " +
+              llvm::toString(std::move(E)));
         return nullptr;
       }
       return llvm::MemoryBuffer::getMemBufferCopy(Uncompressed, Name);
     } else if (RecCode == SM_SLOC_BUFFER_BLOB) {
       return llvm::MemoryBuffer::getMemBuffer(Blob.drop_back(1), Name, true);
     } else {
       Error("AST record has invalid code");
       return nullptr;

lib/Serialization/ASTWriter.cpp

 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Bitcode/BitCodes.h"
 #include "llvm/Bitcode/BitstreamWriter.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Compression.h"
 #include "llvm/Support/EndianStream.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/OnDiskHashTable.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <cassert>
void ASTWriter::WriteHeaderSearch(const HeaderSearch &HS) {
   TableData.append(GeneratorTrait.strings_begin(),GeneratorTrait.strings_end());
   Stream.EmitRecordWithBlob(TableAbbrev, Record, TableData);
   
   // Free all of the strings we had to duplicate.
   for (unsigned I = 0, N = SavedStrings.size(); I != N; ++I)
     free(const_cast<char *>(SavedStrings[I]));
 }
 
+static void emitBlob(llvm::BitstreamWriter &Stream, StringRef Blob,
+                     unsigned SLocBufferBlobCompressedAbbrv,
+                     unsigned SLocBufferBlobAbbrv) {
+  typedef ASTWriter::RecordData::value_type RecordDataType;
+
+  // Compress the buffer if possible. We expect that almost all PCM
+  // consumers will not want its contents.
+  SmallString<0> CompressedBuffer;
+  if (llvm::zlib::isAvailable()) {
+    llvm::Error E = llvm::zlib::compress(Blob.drop_back(1), CompressedBuffer);
+    if (!E) {
+      RecordDataType Record[] = {SM_SLOC_BUFFER_BLOB_COMPRESSED,
+                                 Blob.size() - 1};
+      Stream.EmitRecordWithBlob(SLocBufferBlobCompressedAbbrv, Record,
+                                CompressedBuffer);
+      return;
+    }
+    llvm::consumeError(std::move(E));
+  }
+
+  RecordDataType Record[] = {SM_SLOC_BUFFER_BLOB};
+  Stream.EmitRecordWithBlob(SLocBufferBlobAbbrv, Record, Blob);
+}
+
 /// \brief Writes the block containing the serialized form of the
 /// source manager.
 ///
 /// TODO: We should probably use an on-disk hash table (stored in a
 /// blob), indexed based on the file name, so that we only create
 /// entries for files that we actually need. In the common case (no
 /// errors), we probably won't have to create file entries for any of
 /// the files in the AST.
if (SLoc->isFile()) {
       }
 
       if (EmitBlob) {
         // Include the implicit terminating null character in the on-disk buffer
         // if we're writing it uncompressed.
         const llvm::MemoryBuffer *Buffer =
             Content->getBuffer(PP.getDiagnostics(), PP.getSourceManager());
         StringRef Blob(Buffer->getBufferStart(), Buffer->getBufferSize() + 1);
-
-        // Compress the buffer if possible. We expect that almost all PCM
-        // consumers will not want its contents.
-        SmallString<0> CompressedBuffer;
-        if (llvm::zlib::compress(Blob.drop_back(1), CompressedBuffer) ==
-            llvm::zlib::StatusOK) {
-          RecordData::value_type Record[] = {SM_SLOC_BUFFER_BLOB_COMPRESSED,
-                                             Blob.size() - 1};
-          Stream.EmitRecordWithBlob(SLocBufferBlobCompressedAbbrv, Record,
-                                    CompressedBuffer);
-        } else {
-          RecordData::value_type Record[] = {SM_SLOC_BUFFER_BLOB};
-          Stream.EmitRecordWithBlob(SLocBufferBlobAbbrv, Record, Blob);
-        }
+        emitBlob(Stream, Blob, SLocBufferBlobCompressedAbbrv,
+                 SLocBufferBlobAbbrv);
       }
     } else {
       // The source location entry is a macro expansion.
       const SrcMgr::ExpansionInfo &Expansion = SLoc->getExpansion();
       AddSourceLocation(Expansion.getSpellingLoc(), Record);
       AddSourceLocation(Expansion.getExpansionLocStart(), Record);
       AddSourceLocation(Expansion.isMacroArgExpansion()
                             ? SourceLocation()