libitm: Fix bootstrap for targets without HAVE_ELF_STYLE_WEAKREF.

libitm: Fix bootstrap for targets without HAVE_ELF_STYLE_WEAKREF.

Recent improvements to null address warnings notice that for
targets that do not support HAVE_ELF_STYLE_WEAKREF the dummy stub
implementation of __cxa_get_globals() means that the address can
never be null.

Fixed by removing the test for such targets.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
libitm/ChangeLog:

	* eh_cpp.cc (GTM::gtm_thread::init_cpp_exceptions): If the
	target does not support HAVE_ELF_STYLE_WEAKREF then do not
	try to test the __cxa_get_globals against NULL.