[libunwind] [libunwind][PPC64] Fix _Unwind_Backtrace SIGSEGV from TOC restore at end of stack on LE (PR #212142)

[Fangrui Song via cfe-commits]

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@@ -22,6 +22,15 @@
 #include "dwarf2.h"
 #include "libunwind_ext.h"
 
+#if defined(_LIBUNWIND_TARGET_PPC64) && defined(__BYTE_ORDER__) &&             \
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MaskRay wrote:

If this ELFv2 issue applies big-endian, `defined(_CALL_ELF) && _CALL_ELF == 2`

https://github.com/llvm/llvm-project/pull/212142