__threading_support: Remove (void) in favor of ().
__threading_support: Remove (void) in favor of ().

Summary:
This fixes a clang-tidy warning when building something that uses
this file.

Reviewers: mclow.lists, EricWF

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D43226

git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@364799 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx