Use sysconfig.get_platform for machine detection

This should function correctly when cross compiling unlike
platform.machine.

Author: jameshilliard

.audit/jameshilliard_sysconfig-machine.md

@@ -0,0 +1,10 @@
+## AI Assistance Disclosure
+
+- [x] I did **not** use any AI-assistance tools to help create this pull request.
+- [ ] I **did** use AI-assistance tools to *help* create this pull request.
+- [x] I have read, understood and followed the projects' [AI Policy](https://github.com/crossbario/autobahn-python/blob/main/AI_POLICY.md) when creating code, documentation etc. for this pull request.
+
+Submitted by: @jameshilliard
+Date: 2026-01-01
+Related issue(s): #1834
+Branch: sysconfig-machine

src/autobahn/nvx/_compile_args.py

@@ -124,7 +124,7 @@
 
 import os
 import sys
-import platform
+import sysconfig
 
 
 def is_building_wheel():
@@ -194,7 +194,7 @@ def get_compile_args():
         return ["/O2", "/W3"]
 
     # GCC/Clang on POSIX (Linux, macOS, *BSD)
-    machine = platform.machine().lower()
+    machine = sysconfig.get_platform().lower().split("-")[-1]
 
     # Base flags for all POSIX platforms
     base_args = [