[BUILD] add the USE_GETADDRINFO build option

This one is used to call getaddrinfo() to resolve IPv6 host names.
diff --git a/Makefile.osx b/Makefile.osx
index f60508e..f3ecdb8 100644
--- a/Makefile.osx
+++ b/Makefile.osx
@@ -77,6 +77,7 @@
 # set some defines when needed.
 # Known ones are -DENABLE_POLL
 # - use -DTPROXY to compile with transparent proxy support.
+# - use -DUSE_GETADDRINFO to use of getaddrinfo() to resolve IPv6 host names
 DEFINE = -DTPROXY 
 
 # May be changed to patch PAGE_SIZE on every platform when using dlmalloc