Remove environment sensitivity in pl/tcl regression test.

Add "-gmt 1" to our test invocations of the Tcl "clock" command,
so that they do not consult the timezone environment.  While it
doesn't really matter which timezone is used here, it does
matter that the command not fall over entirely.  We've now
discovered that at least on FreeBSD, "clock scan" will fail if
/etc/localtime is missing.  It seems worth making the test
insensitive to that.

Per Tomas Vondras' buildfarm animal dikkop.  Thanks to
Thomas Munro for the diagnosis.

Discussion: https://postgr.es/m/316d304a-1dcd-cea1-3d6c-27f794727a06@enterprisedb.com

src/pl/tcl/expected/pltcl_setup.out

@@ -119,7 +119,7 @@ CREATE OPERATOR CLASS tcl_int4_ops
 -- for initialization problems.
 --
 create function tcl_date_week(int4,int4,int4) returns text as $$
-    return [clock format [clock scan "$2/$3/$1"] -format "%U"]
+    return [clock format [clock scan "$2/$3/$1" -gmt 1] -format "%U" -gmt 1]
 $$ language pltcl immutable;
 select tcl_date_week(2010,1,26);
  tcl_date_week 

src/pl/tcl/sql/pltcl_setup.sql

@@ -142,7 +142,7 @@ CREATE OPERATOR CLASS tcl_int4_ops
 -- for initialization problems.
 --
 create function tcl_date_week(int4,int4,int4) returns text as $$
-    return [clock format [clock scan "$2/$3/$1"] -format "%U"]
+    return [clock format [clock scan "$2/$3/$1" -gmt 1] -format "%U" -gmt 1]
 $$ language pltcl immutable;
 
 select tcl_date_week(2010,1,26);