Always allow "#pragma region".

Summary:
Both MS and PS4 targets are capable of recognizing the
existence of:  #pragma region, #pragma endregion.

Since this pragma is only a hint for certain editors, and has no logic,
it seems helpful to permit this pragma in all cases, not just MS compatibility mode.



Reviewers: rnk, rsmith, majnemer

Reviewed By: majnemer

Subscribers: Quuxplusone, probinson, majnemer, cfe-commits

Differential Revision: https://reviews.llvm.org/D42248

llvm-svn: 323577