libstdc++: Use nothrow new in std::stacktrace

libstdc++: Use nothrow new in std::stacktrace

We can avoid the overhead of handling a bad_alloc exception from
std::allocator<std::stacktrace_entry>::allocate by just calling the
nothrow operator new instead.

libstdc++-v3/ChangeLog:

	* include/std/stacktrace (basic_stacktrace::_Impl::_M_allocate):
	Use nothrow new instead of try block for std::allocator.
	(basic_stacktrace::_Impl::_M_deallocate): Use delete for
	std::allocator.