[libc++] (Take 2) Correctly handle Objective-C++ ARC qualifiers in std::is_pointer
Summary:
Otherwise, std::is_pointer<id __strong> works, but std::is_pointer<id __weak>
(and others) don't work as expected.
The previous patch (r357517) had to be reverted in r357569 because it
broke the Chromium build. This patch shouldn't have the same problem.
rdar://problem/
49126333
Reviewers: ahatanak, EricWF
Subscribers: christof, jkorous, dexonsmith, libcxx-commits
Differential Revision: https://reviews.llvm.org/D60087
llvm-svn: 357586