libunwind: Enable zero-cost exceptions on non-Apple arm64 platforms

[emaste]

Summary

Use the canonical aarch64 predefined macro for 64-bit ARM. Apple-specific cases are left as arm64. Also add an #error for unsupported architectures to catch this sort of case in the future.

[rengolin]

As discussed in IRC, this has been working on AArch64/Darwin for some time, so any Linux compatibility shall be investigated before creating a buildbot for it (which I'm in the process of doing).

LGTM, thanks!

src/config.h

#else
   static inline void assert_rtn(const char* func, const char* file, int line, const char* msg) {
     fprintf(stderr, "libunwind: %s %s:%d - %s\n",  func, file, line, msg);
     assert(false);
     abort();
   }
 
   #define _LIBUNWIND_BUILD_ZERO_COST_APIS (defined(__i386__) || \
                                            defined(__x86_64__) || \
-                                           defined(__arm__))
+                                           defined(__arm__) || \
+                                           defined(__aarch64__))
   #define _LIBUNWIND_BUILD_SJLJ_APIS      0
   #define _LIBUNWIND_SUPPORT_FRAME_APIS   (defined(__i386__) || \
                                            defined(__x86_64__))
   #define _LIBUNWIND_EXPORT               __attribute__((visibility("default")))
   #define _LIBUNWIND_HIDDEN               __attribute__((visibility("hidden")))
   #define _LIBUNWIND_LOG(msg, ...) fprintf(stderr, "libuwind: " msg, __VA_ARGS__)
   #define _LIBUNWIND_ABORT(msg) assert_rtn(__func__, __FILE__, __LINE__, msg)
 

src/libunwind.cpp

#if defined(__i386__)
   new ((void *)cursor) UnwindCursor<LocalAddressSpace, Registers_x86>(
                                  context, LocalAddressSpace::sThisAddressSpace);
 #elif defined(__x86_64__)
   new ((void *)cursor) UnwindCursor<LocalAddressSpace, Registers_x86_64>(
                                  context, LocalAddressSpace::sThisAddressSpace);
 #elif defined(__ppc__)
   new ((void *)cursor) UnwindCursor<LocalAddressSpace, Registers_ppc>(
                                  context, LocalAddressSpace::sThisAddressSpace);
-#elif defined(__arm64__)
+#elif defined(__arm64__) || defined(__aarch64__)
   new ((void *)cursor) UnwindCursor<LocalAddressSpace, Registers_arm64>(
                                  context, LocalAddressSpace::sThisAddressSpace);
 #elif _LIBUNWIND_ARM_EHABI
   new ((void *)cursor) UnwindCursor<LocalAddressSpace, Registers_arm>(
                                  context, LocalAddressSpace::sThisAddressSpace);
+#else
+#error Architecture not supported
 #endif
   AbstractUnwindCursor *co = (AbstractUnwindCursor *)cursor;
   co->setInfoBasedOnIPRegister();
 
   return UNW_ESUCCESS;
 }
 
 #ifdef UNW_REMOTE