[OpenMP] Move header inclusion out of 'extern "C"'
[OpenMP] Move header inclusion out of 'extern "C"'

This leads to problems when compiling C++ code with libc++ for Nvidia GPUs
because Clang now uses wrappers for math functions that might include
C++ templates not allowed in 'extern "C"'.

Differentiel Revision: https://reviews.llvm.org/D64625

git-svn-id: f99161ee8ccfe2101cbe1bdda2220bce2ed25485@366229 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/openmp,llvm-mirror/openmp,llvm-mirror/openmp,llvm-mirror/openmp,llvm-mirror/openmp