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

[Wu Yingcong via cfe-commits]

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@@ -13,7 +13,9 @@
 
 // clang-format off
 
-// REQUIRES: linux
+// REQUIRES: target={{x86_64-.+-linux-gnu}}
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yingcong-wu wrote:

That is a good suggestion. I will give it a try later.

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