[libFuzzer] Don't short-circuit from CrashCallback.
[libFuzzer] Don't short-circuit from CrashCallback.

Short-circuiting causes tests to fail on Mac since libFuzzer crashes
rather than exiting with an error code when an unexpected signal
happens.

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@331324 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt