libfuzzer: fix compiler warnings

- unused sigaction/setitimer result (used in assert)
- unchecked fscanf return value
- signed/unsigned comparison



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@262472 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed