clib: update C/C++ copyright statements to pass lint checks
Update the copyright headers in most of the C/C++ code consistently use the
GPLv2 copyright message. This allows these files to pass Facebook's internal
Some of the files in fbcode/scm/hgext/cstore/ appear to have actually been
copied from the hg-crew repository, and were not originally authored by
Facebook. I have not modified the copyright statements in these files:
I also have not modified any of the cfastmanifest code.
This corresponds to Facebook diff D5588677.
Confirmed that Facebook's C++ linters no longer complain about the copyright
Reviewers: #fbhgext, quark
Reviewed By: #fbhgext, quark
Differential Revision: https://phab.mercurial-scm.org/D507