Merging r292590:

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r292590 | abataev | 2017-01-20 00:57:28 -0800 (Fri, 20 Jan 2017) | 6 lines

[OPENMP] Fix for PR31643: Clang crashes when compiling code on Windows
with SEH and openmp

In some cituations (during codegen for Windows SEH constructs)
CodeGenFunction instance may have CurFn equal to nullptr. OpenMP related
code does not expect such situation during cleanup.
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git-svn-id: https://llvm.org/svn/llvm-project/cfe/branches/release_40@293302 91177308-0d34-0410-b5e6-96231b3b80d8