Restore attributions for fnmatch

The fnmatch function came from OpenBSD via AOSP - adding back the copyright statements as per the terms of their original licenses. Note that this is restoring the headers included in the file when originally brought over at libgit2/libgit2@e9c6571d7fd39c82232fd965544ce34c6974a441 but look to have been accidentally dropped from the files during libgit2/libgit2@824d5e4d260fc740dbe9251008439b9e58db5f19.