HAVE_SYS_AUXV_H check should be changed to HAVE_GETAUXVAL and
HAVE_ELF_AUX_INFO. For now this works.

Index: libunwind/src/Registers.hpp
--- libunwind/src/Registers.hpp.orig
+++ libunwind/src/Registers.hpp
@@ -1943,7 +1943,12 @@ class _LIBUNWIND_HIDDEN Registers_arm64 { (private)
 #if defined(_LIBUNWIND_HAVE_GETAUXVAL)
   static bool checkHasSME() {
     constexpr int hwcap2_sme = (1 << 23);
+#if defined(__OpenBSD__)
+    unsigned long hwcap2 = 0;
+    elf_aux_info(AT_HWCAP2, &hwcap2, sizeof(hwcap2));
+#else
     unsigned long hwcap2 = getauxval(AT_HWCAP2);
+#endif
     return (hwcap2 & hwcap2_sme) != 0;
   }
 #elif defined(_LIBUNWIND_HAVE_ELF_AUX_INFO)
