[Unwind][AArch64] Match sigreturn instructions in big endian (#167139)

Since insns are always stored LE, on a BE system the opcodes will be
loaded byte-reversed. Therefore, define two sets of opcodes, one for LE
and one for BE.

NOKEYCHECK=True
GitOrigin-RevId: 6214dccbc991abe5a1679bc88e74b8c7d53f3d45

src/UnwindCursor.hpp

diff --git a/src/UnwindCursor.hpp b/src/UnwindCursor.hpp
index d734825..33fcd84 100644
--- a/src/UnwindCursor.hpp
+++ b/src/UnwindCursor.hpp
@@ -2865,6 +2865,21 @@
 
 #if defined(_LIBUNWIND_CHECK_LINUX_SIGRETURN) &&                               \
     defined(_LIBUNWIND_TARGET_AARCH64)
+
+/*
+ * The linux sigreturn restorer stub will always have the form:
+ *
+ *  d2801168        movz    x8, #0x8b
+ *  d4000001        svc     #0x0
+ */
+#if defined(__AARCH64EB__)
+#define MOVZ_X8_8B 0x681180d2
+#define SVC_0 0x010000d4
+#else
+#define MOVZ_X8_8B 0xd2801168
+#define SVC_0 0xd4000001
+#endif
+
 template <typename A, typename R>
 bool UnwindCursor<A, R>::setInfoForSigReturn(Registers_arm64 &) {
   // Look for the sigreturn trampoline. The trampoline's body is two
@@ -2889,7 +2904,7 @@
     return false;
   auto *instructions = reinterpret_cast<const uint32_t *>(pc);
   // Look for instructions: mov x8, #0x8b; svc #0x0
-  if (instructions[0] != 0xd2801168 || instructions[1] != 0xd4000001)
+  if (instructions[0] != MOVZ_X8_8B || instructions[1] != SVC_0)
     return false;
 
   _info = {};