Fix dbghelp for AArch64. (#270)

Intel Itanium is not the same as ARM 64.
I don't have any device with Windows and ARM to test it, but at least
this compiles now.

---------

Co-authored-by: Jeremy Rifkin <51220084+jeremy-rifkin@users.noreply.github.com>

Author: mcourteaux

src/unwind/unwind_with_dbghelp.cpp

@@ -86,7 +86,7 @@ namespace detail {
         frame.AddrFrame.Mode   = AddrModeFlat;
         frame.AddrStack.Offset = context.Rsp;
         frame.AddrStack.Mode   = AddrModeFlat;
-        #elif defined(_M_IA64) || defined(__aarch64__)
+        #elif defined(_M_IA64)
         machine_type           = IMAGE_FILE_MACHINE_IA64;
         frame.AddrPC.Offset    = context.StIIP;
         frame.AddrPC.Mode      = AddrModeFlat;
@@ -96,6 +96,14 @@ namespace detail {
         frame.AddrBStore.Mode  = AddrModeFlat;
         frame.AddrStack.Offset = context.IntSp;
         frame.AddrStack.Mode   = AddrModeFlat;
+        #elif defined(_M_ARM64) || defined(__aarch64__)
+        machine_type           = IMAGE_FILE_MACHINE_ARM64;
+        frame.AddrPC.Offset    = context.Pc;
+        frame.AddrPC.Mode      = AddrModeFlat;
+        frame.AddrFrame.Offset = context.Fp;
+        frame.AddrFrame.Mode   = AddrModeFlat;
+        frame.AddrStack.Offset = context.Sp;
+        frame.AddrStack.Mode   = AddrModeFlat;
         #else
         #error "Cpptrace: StackWalk64 not supported for this platform yet"
         #endif