Replace a few strncmp() calls with strlcpy().

strncmp() is a specialized API unsuited for routine copying into
fixed-size buffers.  On a system where the length of a single filename
can exceed MAXPGPATH, the pg_archivecleanup change prevents a simple
crash in the subsequent strlen().  Few filesystems support names that
long, and calling pg_archivecleanup with untrusted input is still not a
credible use case.  Therefore, no back-patch.

David Rowley

src/backend/access/transam/xlogarchive.c

@@ -459,7 +459,8 @@ KeepFileRestoredFromArchive(char *path, char *xlogfname)
 							xlogfpath, oldpath)));
 		}
 #else
-		strncpy(oldpath, xlogfpath, MAXPGPATH);
+		/* same-size buffers, so this never truncates */
+		strlcpy(oldpath, xlogfpath, MAXPGPATH);
 #endif
 		if (unlink(oldpath) != 0)
 			ereport(FATAL,