Revert "Make BitCodeAbbrev ownership explicit using shared_ptr rather than IntrusiveRefCntPtr"

Breaks Clang's use of bitcode. Reverting until I have a fix to go with
it there.

This reverts commit r291006.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291007 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Bitcode/Reader/BitstreamReader.cpp

@@ -273,7 +273,7 @@ unsigned BitstreamCursor::readRecord(unsigned AbbrevID,
 }
 
 void BitstreamCursor::ReadAbbrevRecord() {
-  auto Abbv = std::make_shared<BitCodeAbbrev>();
+  BitCodeAbbrev *Abbv = new BitCodeAbbrev();
   unsigned NumOpInfo = ReadVBR(5);
   for (unsigned i = 0; i != NumOpInfo; ++i) {
     bool IsLiteral = Read(1);
@@ -307,7 +307,7 @@ void BitstreamCursor::ReadAbbrevRecord() {
 
   if (Abbv->getNumOperandInfos() == 0)
     report_fatal_error("Abbrev record with no operands");
-  CurAbbrevs.push_back(std::move(Abbv));
+  CurAbbrevs.push_back(Abbv);
 }
 
 Optional<BitstreamBlockInfo>