Fix hardware detection on aix.

configure

@@ -2505,14 +2505,18 @@ windres_default="windres"
 
 nogas=":"
 
-# machine
-arch_default=$(uname -m)
-cpu="generic"
-
 # OS
 target_os_default=$(tolower $(uname -s))
 host_os=$target_os_default
 
+# machine
+if test "$target_os_default" = aix; then
+    arch_default=$(uname -p)
+else
+    arch_default=$(uname -m)
+fi
+cpu="generic"
+
 # configurable options
 enable $PROGRAM_LIST
 enable $DOCUMENT_LIST