[DebugInfo][test] XFAIL DebugInfo/Generic/no-empty-child-vars.ll on SPARC

`DebugInfo/Generic/no-empty-child-vars.ll` `FAIL`s on SPARC.  As discussed
in D95617 <https://reviews.llvm.org/D95617>, this is yet another instance
of Issue #46473.

As was done for other failures due to this bug, this patch `XFAIL`s the test.

Tested on `sparcv9-sun-solaris2.11`.

Differential Revision: https://reviews.llvm.org/D120238