[NFC][OpenMP] Add new test for parallel for code generation.
[NFC][OpenMP] Add new test for parallel for code generation.

Summary:
This is a simple test of the parallel for code generation. It will be used to showcase the change introduced by patch D53443.


Reviewers: ABataev, caomhin

Reviewed By: ABataev

Subscribers: guansong, cfe-commits

Differential Revision: https://reviews.llvm.org/D53772

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@345417 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang