[libc++] Make sure that the symbol differ takes into account symbol types

Summary:
Otherwise, it doesn't take into account things like whether the symbol
is defined or undefined, and whether symbols are indirect references
(re-exports) or not.

Reviewers: EricWF

Subscribers: christof, jkorous, dexonsmith, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D60416

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@358408 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed