Use int64_t instead of la_int64_t

Resolve error reported on irc with Ubuntu (don't know what version):
<rjwboys> ok now i get filedat.c:896:3: error: unknown type name ‘la_int64_t’

src/sbbs3/filedat.c

@@ -893,7 +893,7 @@ long extract_files_from_archive(const char* archive, const char* outdir, const c
 
 		const void *buff;
 		size_t size;
-		la_int64_t offset;
+		int64_t offset;
 
 		for(;;) {
 			result = archive_read_data_block(ar, &buff, &size, &offset);