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/YAMLRemarkSerializer.cpp b/llvm/lib/Remarks/YAMLRemarkSerializer.cpp
index f8ed740..c4a5bcc 100644
--- a/llvm/lib/Remarks/YAMLRemarkSerializer.cpp
+++ b/llvm/lib/Remarks/YAMLRemarkSerializer.cpp
@@ -191,7 +191,7 @@
 static void emitVersion(raw_ostream &OS) {
   // Emit the version number: little-endian uint64_t.
   std::array<char, 8> Version;
-  support::endian::write64le(Version.data(), remarks::Version);
+  support::endian::write64le(Version.data(), remarks::CurrentRemarkVersion);
   OS.write(Version.data(), Version.size());
 }