[libFuzzer tests] Use substring comparison in libFuzzer tests

LIT launches executables with absolute, and not relative, path.
strncmp would try to do exact comparison and fail.

Differential Revision: https://reviews.llvm.org/D36242

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@309889 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed