swift234

[mangle] Add support for mangling dead, owned2guaranteed, and sroa args. Wire up function sig opts.

Now all SIL function specialization passes use the new mangling infrastructure.
Lets keep it that way for future passes as well. = ).

Implements:
<rdar://problem/18831609>

Fixes:
<rdar://problem/19065735>
<rdar://problem/18906781>
<rdar://problem/18956916>

Swift SVN r23859