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

[Alastair Houghton via cfe-commits]

================
@@ -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
+//
----------------
al45tair wrote:

Let's rearrange it to use `XFAIL`, since that's clearer.

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