gdb: allow enumeration constants as second operand of BINOP_REPEAT

gdb: allow enumeration constants as second operand of BINOP_REPEAT

This patch adds support for TYPE_CODE_ENUM values to be supplied
as right-hand side operand of the BINOP_REPEAT (@) operator. The
following should now work:

enum {
  sz = 17
};

int
main ()
{
  int arr[sz + 1] = { 0 };
  return 0; /* line 9 here */
}

(gdb) b 9
(gdb) r
(gdb) p arr@sz
$1 = {0 <repeats 17 times>}
(gdb)

A couple of tests is also included in this patch to demonstrate that it is
working as intended.

gdb/Changelog:

2016-04-01  Artemiy Volkov  <artemiyv@acm.org>

	PR gdb/19820
	* eval.c (evaluate_subexp_standard): Allow TYPE_CODE_ENUM to be
        the type of BINOP_REPEAT's second operand.

gdb/testsuite/Changelog:

2016-04-01  Artemiy Volkov  <artemiyv@acm.org>

	PR gdb/19820
	* gdb.base/printcmds.exp: Add artificial arrays tests.