[libunwind] [libunwind] Tweak tests for musl support. (PR #85097)

[Alastair Houghton via cfe-commits]

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@@ -24,16 +23,30 @@
 #include <unistd.h>
 #include <unwind.h>
 
+// Note: this test fails on musl because:
+//
+//  (a) musl disables emission of unwind information for its build, and
+//  (b) musl's signal trampolines don't include unwind information
+//
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al45tair wrote:

We'll use `XFAIL` here too.

https://github.com/llvm/llvm-project/pull/85097