This allows the usage of the whole remark infrastructure developed in
LLVM, which includes a new binary format, metadata in object files, etc.
This gets rid of the YAMLTraits-based remark serialization and does the
plumbing for hooking to LLVM's main remark streamer.
For more about the idea behind LLVM's main remark streamer, see the
docs/Remarks.rst changes in https://reviews.llvm.org/D73676.
The flags are now:
* -save-optimization-record: enable remarks, defaults to YAML
* -save-optimization-record=<format>: enable remarks, use <format> for
serialization
* -save-optimization-record-passes <regex>: only serialize passes that
match <regex>.
The YAMLTraits in swift had a different `flow` setting for the debug
location, resulting in some test changes.
This brings the capability from clang to save remarks in an external YAML files.
YAML files can be viewed with tools like the opt-viewer.
Saving the remarks is activated with the new option -save-optimization-record.
Similarly to -emit-tbd, I've only added support for single-compile mode for now.
In this case the default filename is determined by
getOutputFilenameFromPathArgOrAsTopLevel, i.e. unless explicitly specified
with -save-optimization-record-path, the file is placed in the directory of the
main output file as <modulename>.opt.yaml.
