[ObjC] Make C++ triviality type traits available to non-trivial C

[ObjC] Make C++ triviality type traits available to non-trivial C
structs.

r326307 and r327870 made changes that allowed using non-trivial C
structs with fields qualified with __strong or __weak. This commit makes
the following C++ triviality type traits available to non-trivial C
structs:

__has_trivial_assign
__has_trivial_move_assign
__has_trivial_copy
__has_trivial_move_constructor
__has_trivial_constructor
__has_trivial_destructor

rdar://problem/33599681

Differential Revision: https://reviews.llvm.org/D44913

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@328680 91177308-0d34-0410-b5e6-96231b3b80d8