Fix detection of default architecture

build.py

@@ -322,6 +322,16 @@ def setDevModeOptions(args):
     # anybody besides Robin is using this option do not depend on the options
     # it inserts into the args list being consistent. They could change at any
     # update from the repository.
+    if isDarwin:
+        import platform
+        proc = platform.processor()
+        if proc == 'i386':
+            proc = 'x86_64'
+        if proc == 'arm':
+            proc = 'arm64'
+    else:
+        proc = 'unk'
+
     myDevModeOptions = [
             #'--build_dir=../bld',
             #'--prefix=/opt/wx/2.9',
@@ -330,7 +340,7 @@ def setDevModeOptions(args):
             # These will be ignored on the other platforms so it is okay to
             # include them unconditionally
             '--osx_cocoa',
-            '--mac_arch=x86_64',
+            '--mac_arch={}'.format(proc),
             '--no_allmo',
             ]
     if not isWindows: