llvm-readobj: fix endianness

Explicitly handle endianness to ensure that bytes are read properly on
big-endian systems.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198847 91177308-0d34-0410-b5e6-96231b3b80d8
llvm-readobj: address review comments for ARM EHABI printing

Rename bytecode to opcodes to make it more clear.  Change an impossible case to
llvm_unreachable instead.  Avoid allocation of a buffer by modifying the
PrintOpcodes iteration.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198848 91177308-0d34-0410-b5e6-96231b3b80d8