#pragma weak, global register variables and static initialization of flexible
array members are supported now, so they are removed from "GCC extensions not
implemented yet" list.

Differential Revision: http://reviews.llvm.org/D16851


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@260506 91177308-0d34-0410-b5e6-96231b3b80d8