[lldb] Require x86 for unwind no-return test

The core file used is built for i386 so we
need the x86 backend to be able to load it.

Reviewed By: labath

Differential Revision: https://reviews.llvm.org/D100195

GitOrigin-RevId: a1f3187ca8a39a62f4a430da823c01aa7874b0d3
1 file changed