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

In #154902, the test failed
with llvm-clang-win-x-aarch64(it is a cross-build, which builds on
Windows and run on Linux, "Win to Aarch64 Linux Ubuntu Cross
Toolchain"), and objdump is not available on Windows(the build env).
Set to require x86 Linux instead.

Author: yingcong-wu

libunwind/test/eh_frame_fde_pc_range.pass.cpp

@@ -13,7 +13,9 @@
 
 // clang-format off
 
-// REQUIRES: linux
+// REQUIRES: target={{x86_64-.+-linux-gnu}}
+// aarch64,arm have a cross toolchain build(llvm-clang-win-x-aarch64, etc)
+// where objdump is not available.
 
 // TODO: Figure out why this fails with Memory Sanitizer.
 // XFAIL: msan