SjLj: Fix building after SVN r314632
SjLj: Fix building after SVN r314632

The code moved from Unwind_AppleExtras.cpp to Unwind-sjlj.c needed
a few minor modifications to build as C instead of C++.

git-svn-id: 62ef012455b6b8fcec9c41ca270ebf409aae1006@314635 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libunwind,llvm-mirror/libunwind,llvm-mirror/libunwind