llvm-readobj: call exit(1) on error.

llvm-readobj: call exit(1) on error.

llvm-readobj exists for testing llvm. We can safely stop the program
the first time we know the input in corrupted.

This is in preparation for making it handle a few more broken files.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242656 91177308-0d34-0410-b5e6-96231b3b80d8