Add OpenSolaris compatibility definitions for stat64 and fstat64 which

Add OpenSolaris compatibility definitions for stat64 and fstat64 which
are only visible if _SOLARIS_C_SOURCE is defined.

Note thar FreeBSD stat() and fstat() are 64-bit functions now and Solaris
still persists with both 32- and 64-bit versions. When I query this, I am
referred to: <http://www.unix.org/version2/whatsnew/lfs20mar.html>.
But when you look at the main page of unix.org you will see that the
Single Unix Specification <http://www.unix.org/version3/> is the most
recent standard they are pushing. And there are no stat64() fstat64()
functions defined there. I guess this just goes to prove that there are so
many standards, you can take your pick.