Use the new LLVM_END_WITH_NULL name

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@221217 91177308-0d34-0410-b5e6-96231b3b80d8
[llvm-api-change] Use findProgramByName.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@221222 91177308-0d34-0410-b5e6-96231b3b80d8