lua: add legacy-support for Tiger

Lua uses `localtime_r` and `gmtime_r`, which require legacy-support
on Tiger.

lang/lua/Portfile

@@ -1,6 +1,7 @@
 # -*- coding: utf-8; mode: tcl; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- vim:fenc=utf-8:ft=tcl:et:sw=4:ts=4:sts=4
 
 PortSystem                  1.0
+PortGroup                   legacysupport 1.1
 PortGroup                   makefile    1.0
 
 # each version of Lua can (and does) break backwards compatibility
@@ -37,6 +38,9 @@ checksums                   rmd160  cc715df991bccaec75a022404902200d984b002e \
                             sha256  fc5fd69bb8736323f026672b1b7235da613d7177e72558893a0bdcd320466d60 \
                             size    303770
 
+# localtime_r gmtime_r
+legacysupport.newest_darwin_requires_legacy 8
+
 # Semantic Versioning uses x.y.z as the "version"
 # in the Lua nomenclature, x.y is the version and z is the release
 #     this causes notation conflict within the port