Fix EHFrame processing to add implicit references when needed.

The current code for processCIE and processFDE returns out if it sees
any references.  The problem with this is that some references could be
explicit in the binary, while others are implicit as they can be
inferred from the content of the EHFrame itself.

This change walks the references we have against the references we
need, and verifies that all explicit references are in the correct place,
and generates any missing implicit ones.

Reviewed by Lang Hames and Nick Kledzik.

Differential Revision: http://reviews.llvm.org/D15439

llvm-svn: 263590