[CommonML] Export the SUFFIX flags into the .merlin file.
[CommonML] Export the SUFFIX flags into the .merlin file.

Summary: I have a pull request open for merlin which will allow merlin
to use the SUFFIX flags when looking up file locations on disk. This is
nice if you have a custom extension like myFile.ml.cpp etc.

Test Plan:

Reviewers:

CC:

jordwalke/CommonML,jordwalke/CommonML