tmdata: prioritise "UTC" over "GMT"

"UTC" is the modern name for what used to be "GMT", but ksh still
preferred GMT. On systems configured to use the UTC time zone, this
caused a 'printf %T' regression test failure in tests/builtins.sh
as the external 'data' utility will prefer UTC these days.

src/lib/libast/tm/tmdata.c:
- Reorder the name alternatives for UTC/GMT so that UTC is
  the first preference.

src/cmd/ksh93/tests/builtins.sh:
- Report expected and actual values on 'printf %T' failure.

Related: #6

src/cmd/ksh93/tests/builtins.sh

@@ -310,9 +310,10 @@ then	err_exit "printf '%..*s' not working"
 fi
 [[ $(printf '%q\n') == '' ]] || err_exit 'printf "%q" with missing arguments'
 # we won't get hit by the one second boundary twice, right?
-[[ $(LC_ALL=C printf '%T\n' now) == "$(LC_ALL=C date)" ]] ||
-[[ $(LC_ALL=C printf '%T\n' now) == "$(LC_ALL=C date)" ]] ||
-err_exit 'printf "%T" now'
+expect= actual=
+{ expect=$(LC_ALL=C date) && actual=$(LC_ALL=C printf '%T\n' now) && [[ $actual == "$expect" ]]; } ||
+{ expect=$(LC_ALL=C date) && actual=$(LC_ALL=C printf '%T\n' now) && [[ $actual == "$expect" ]]; } ||
+err_exit 'printf "%T" now' "(expected $(printf %q "$expect"), got $(printf %q "$actual"))"
 behead()
 {
 	read line

src/lib/libast/tm/tmdata.c

@@ -54,7 +54,7 @@ static char*		format[] =
 
 	"AM",		"PM",
 
-	"GMT",		"UTC",		"UCT",		"CUT",
+	"UTC",		"UCT",		"CUT",		"GMT",
 
 	"DST",		"",		"",		"",
 
@@ -233,10 +233,10 @@ static Tm_leap_t	leap[] =
 
 static Tm_zone_t	zone[] =
 {
- 0,	"GMT",	0,	 ( 0 * 60),	     0,	/* UTC			*/
- 0,	"UCT",	0,	 ( 0 * 60),	     0,	/* UTC			*/
  0,	"UTC",	0,	 ( 0 * 60),	     0,	/* UTC			*/
+ 0,	"UCT",	0,	 ( 0 * 60),	     0,	/* UTC			*/
  0,	"CUT",	0,	 ( 0 * 60),	     0,	/* UTC			*/
+ 0,	"GMT",	0,	 ( 0 * 60),	     0,	/* UTC			*/
  0,	"Z",	0,	 ( 0 * 60),	     0,	/* UTC			*/
  "USA",	"HST",	0,	 (10 * 60),	     0,	/* Hawaii		*/
  0,	"YST",	"YDT",	 ( 9 * 60),	TM_DST,	/* Yukon		*/