This code adds some simple decoding of the FDE's in an eh_frame.
There's still more to be done in terms of error handling and verification.
Also, we need to be able to decode the CFI's.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255550 91177308-0d34-0410-b5e6-96231b3b80d8