[DebugInfo][test] Check specific func name to ignore codegen differences

We use `CHECK-LABEL: define` to divide input stream into functions,
this works well on most platforms.

But there are cases that some platforms (eg: AIX) may have different
codegen , especially for global constructor and descructors.

On AIX, the codegen will have two more functions: __dtor_b,
__finalize_b, which will fail the test.

The fix is to use specific function name so that we can safely ignore
those unrelated codegen differences.

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D102654