Fix PR25101 - Handle anonymous functions without VST entries

Summary:
The change to use the VST function entries for lazy deserialization did
not handle the case of anonymous functions without aliases. In that case
we must fall back to scanning the function blocks as there is no VST
entry.

Reviewers: dexonsmith, joker.eph, davidxl

Subscribers: tstellarAMD, llvm-commits

Differential Revision: http://reviews.llvm.org/D13596

llvm-svn: 249947