clang/test/CodeGenCXX/builtins.cpp: Fix for -Asserts.

  - Don't seek "entry:" It dosen't appear with -Asserts.
  - Take care that Codegen'ed Instruction(s) wouldn't have name(s) in -Asserts.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193908 91177308-0d34-0410-b5e6-96231b3b80d8