This is follow-up of https://bugs.llvm.org/show_bug.cgi?id=35945, which reports that libc++ doesn't build for the Raspberry PI.
Errors related to char are fixed now, but there are some missing values from _Unwind_Reason_Code enum and wrong behavior of _US_FORCE_UNWIND
this is taken (with permission) from: https://src.fedoraproject.org/rpms/v8/blob/master/f/v8-6.7.17-fix-gcc-unwind-header.patch
Not sure about who should review this, so I added all reviewers from D42242
The reason this went unnoticed for so long is that allmost all distros use clang to build their libcxx/libcxxabi package, which passes fine.