Updated llvm-proto-fuzzer to execute the compiled code

Updated llvm-proto-fuzzer to execute the compiled code

Summary:
Made changes to the llvm-proto-fuzzer
- Added loop vectorizer optimization pass in order to have two IR versions
- Updated old fuzz target to handle two different IR versions
- Wrote code to execute both versions in memory

Reviewers: morehouse, kcc, alexshap

Reviewed By: morehouse

Subscribers: pcc, mgorny, cfe-commits, llvm-commits

Differential Revision: https://reviews.llvm.org/D49526

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@338077 91177308-0d34-0410-b5e6-96231b3b80d8