Set print symbol off in some tests

Set print symbol off in some tests

GDB in default prints the symbol associated on an address, and tests
assume that there is no symbol on address zero.  However, on bare
metal target, address may be mapped to zero and there may be a
symbol.  Then, some tests fail as below:

print const_cast<void *> (0)^M
$8 = (void *) 0x0 <_ftext>^M
(gdb) FAIL: gdb.cp/casts.exp: const_cast of 0

p acp->c1^M
$9 = (A *) 0x0 <_ftext>^M
(gdb) FAIL: gdb.cp/class2.exp: p acp->c1

This patch is to set print symbol off in these tests, like what
I did previously https://sourceware.org/ml/gdb-patches/2014-07/msg00257.html

gdb/testsuite:

2014-08-15  Yao Qi  <yao@codesourcery.com>

	* gdb.cp/casts.exp: Set print symbol off.
	* gdb.cp/class2.exp: Likewise.
	* gdb.cp/overload.exp: Likewise.
	* gdb.cp/templates.exp: Likewise.