[docs] Mention that SjLj works on any OS on the archs where supported by the compiler
[docs] Mention that SjLj works on any OS on the archs where supported by the compiler

Differential Revision: https://reviews.llvm.org/D38576

git-svn-id: 62ef012455b6b8fcec9c41ca270ebf409aae1006@315090 91177308-0d34-0410-b5e6-96231b3b80d8

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