[OPENMP] Support for codegen of private clause of target, host side

This patch adds support for codegen of private clause of target and a regression test for host code generation, when the host is used as target device. I believe that code generation for nvptx backend would not require anything additional or different to what is done for the host.

http://reviews.llvm.org/D18105




git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@263654 91177308-0d34-0410-b5e6-96231b3b80d8