Fix fails in gdb.trace/unavailable.exp

Fix fails in gdb.trace/unavailable.exp

I am seeing some test fails in gdb.trace/unavailable.exp on aarch64-linux,
like this,

print derived_whole^M
$43 = (Derived) {<Middle> = {<Base> = {x = 2}, _vptr.Middle = 0x401860 <VTT for Derived>, y = 3}, _vptr.Derived = 0x401848 <vtable for Derived+32>, z = 4}^M
(gdb) FAIL: gdb.trace/unavailable.exp: collect globals: print object on: print derived_whole

print derived_whole^M
$47 = {<Middle> = {<Base> = {x = 2}, _vptr.Middle = 0x401860 <VTT for Derived>, y = 3}, _vptr.Derived = 0x401848 <vtable for Derived+32>, z = 4}^M
(gdb) FAIL: gdb.trace/unavailable.exp: collect globals: print object off: print derived_whole

these fails are also found by recent x86_64-linux buildbot,
https://sourceware.org/ml/gdb-testers/2016-q2/msg00622.html

The fix is exactly the same as this one
http://www.sourceware.org/ml/gdb-patches/2015-10/msg00252.html (the
extra "VTT" after hex), in which we match extra things after $hex.

gdb/testsuite:

2016-04-22  Yao Qi  <yao.qi@linaro.org>

	* gdb.trace/unavailable.exp (gdb_collect_globals_test_1): Match
	more after $hex.