[libFuzzer] Dump trace and provide correct msg for overwritten input.

Summary:
Now crashes with a stacktrace and uses 'overwrites-const-input' as the error
message instead of 'out-of-memory'.

Reviewers: morehouse, Dor1s

Reviewed By: morehouse, Dor1s

Subscribers: #sanitizers, llvm-commits, metzman, Dor1s

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D68067

llvm-svn: 373130