Make BitCodeAbbrev ownership explicit using shared_ptr rather than IntrusiveRefCntPtr

If this is a problem for anyone (shared_ptr is two pointers in size,
whereas IntrusiveRefCntPtr is 1 - and the ref count control block that
make_shared adds is probably larger than the one int in RefCountedBase)
I'd prefer to address this by adding a lower-overhead version of
shared_ptr (possibly refactoring IntrusiveRefCntPtr into such a thing)
to avoid the intrusiveness - this allows memory ownership to remain
orthogonal to types and at least to me, seems to make code easier to
understand (since no implicit ownership acquisition can happen).

llvm-svn: 291006

llvm/unittests/Bitcode/BitstreamReaderTest.cpp

@@ -101,10 +101,10 @@ TEST(BitstreamReaderTest, readRecordWithBlobWhileStreaming) {
       Stream.Emit(Magic, 32);
       Stream.EnterSubblock(BlockID, 3);
 
-      BitCodeAbbrev *Abbrev = new BitCodeAbbrev();
+      auto Abbrev = std::make_shared<BitCodeAbbrev>();
       Abbrev->Add(BitCodeAbbrevOp(RecordID));
       Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Blob));
-      AbbrevID = Stream.EmitAbbrev(Abbrev);
+      AbbrevID = Stream.EmitAbbrev(std::move(Abbrev));
       unsigned Record[] = {RecordID};
       Stream.EmitRecordWithBlob(AbbrevID, makeArrayRef(Record), BlobIn);