[libunwind] [libunwind][test] set fed test to require x86 as others arch may have cross toolchain build (PR #156383)

[Wu Yingcong via cfe-commits]

yingcong-wu wrote:

I admit that this test is not well-written, but it is also hard to write the test that meet the condition. If we simply does not emit .eh_frame_hdr section, then libunwind simply won't work because it gets the .eh_frame addr from it. And I don't have any clue how to make the linker generate a .eh_frame_hdr that only contains the .eh_frame addr and no search table. I would happily open to any suggestions.

https://github.com/llvm/llvm-project/pull/156383