Process the isolated-build config earlier

The set_config_opts_per_cmdline() method operates with
config_opts['target_arch'], and we need to read the previously chosen
target_arch before that.

mock/py/mockbuild/config.py

@@ -413,6 +413,8 @@ def multiply_platform_multiplier(config_opts):
 def set_config_opts_per_cmdline(config_opts, options, args):
     "takes processed cmdline args and sets config options."
 
+    process_isolated_build_config(options, config_opts)
+
     cli_opt_new = {}
     for cli_opt in options.cli_config_opts:
         k, v = cli_opt.split("=", 1)
@@ -654,8 +656,6 @@ def set_config_opts_per_cmdline(config_opts, options, args):
     if config_opts["calculatedeps"]:
         config_opts["plugin_conf"]["buildroot_lock_enable"] = True
 
-    process_isolated_build_config(options, config_opts)
-
 def check_config(config_opts):
     if 'root' not in config_opts:
         raise exception.ConfigError("Error in configuration "