Reland: [Remarks] Add an LLVM-bitstream-based remark serializer

Add a new serializer, using a binary format based on the LLVM bitstream
format.

This format provides a way to serialize the remarks in two modes:

1) Separate mode: the metadata is separate from the remark entries.
2) Standalone mode: the metadata and the remark entries are in the same
file.

The format contains:

* a meta block: container version, container type, string table,
external file path, remark version
* a remark block: type, remark name, pass name, function name, debug
file, debug line, debug column, hotness, arguments (key, value, debug
file, debug line, debug column)

A string table is required for this format, which will be dumped in the
meta block to be consumed before parsing the remark blocks.

On clang itself, we noticed a size reduction of 13.4x compared to YAML,
and a compile-time reduction of between 1.7% and 3.5% on CTMark.

Differential Revision: https://reviews.llvm.org/D63466

Original llvm-svn: 367364
Revert llvm-svn: 367370

llvm-svn: 367372
diff --git a/llvm/lib/Remarks/YAMLRemarkParser.cpp b/llvm/lib/Remarks/YAMLRemarkParser.cpp
index 0b11523..7b1e4d7 100644
--- a/llvm/lib/Remarks/YAMLRemarkParser.cpp
+++ b/llvm/lib/Remarks/YAMLRemarkParser.cpp
@@ -75,11 +75,11 @@
   uint64_t Version =
       support::endian::read<uint64_t, support::little, support::unaligned>(
           Buf.data());
-  if (Version != remarks::Version)
+  if (Version != remarks::CurrentRemarkVersion)
     return createStringError(std::errc::illegal_byte_sequence,
                              "Mismatching remark version. Got %" PRId64
                              ", expected %" PRId64 ".",
-                             Version, remarks::Version);
+                             Version, remarks::CurrentRemarkVersion);
   Buf = Buf.drop_front(sizeof(uint64_t));
   return Version;
 }