LWG2442: call_once() shouldn't DECAY_COPY(). Patch from K-Ballo.

This patch fixes LWG issue 2422 by removing the DECAY_COPY from call once.
The review can be found here: http://reviews.llvm.org/D10191


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@239654 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed