legacysupport-1.1 PG: Update default newest OS to Darwin 18

Commit 9180c45 overlooked the fact that there are two versions of
the legacysupport PG, and only updated v1.0.  This makes the
equivalent change to v1.1.

_resources/port1.0/group/legacysupport-1.1.tcl

@@ -21,8 +21,8 @@ namespace eval legacysupport {
 }
 
 # Newest Darwin version that requires legacy support.
-# Currently OS X 10.12 ( Sierra, Darwin 16) due to utimensat, fsgetpath, setattrlistat
-set ls_max_darwin_support 16
+# Currently OS X 10.14 ( Mojave, Darwin 18) due to timespec_get
+set ls_max_darwin_support 18
 options legacysupport.newest_darwin_requires_legacy
 default legacysupport.newest_darwin_requires_legacy ${ls_max_darwin_support}