[libFuzzer] Don't replace custom signal handlers.

Summary:
This allows to keep handlers installed by sanitizers.
In other cases third-party code can replace handlers after libFuzzer
initialization anyway.

Reviewers: kcc

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33522

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@303828 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed