Re-commit the changes from r282565 that I had to back out because of

a linux bot test failure.  That one is fixed; hopefully there won't
be any others turned up this time.

The eh_frame augmentation code wasn't working right after the 
reorg/rewrite of the classes.  It works correctly now for the one
test that was failing - but we'll see what the test bots come up
with. 

<rdar://problem/28509178> 

llvm-svn: 282659