mx.fastr: revert junit_* definitions to allow override

mx.fastr/mx_fastr.py

@@ -370,19 +370,19 @@ def junit(args):
     return mx_fastr_junit.junit(args, _junit_r_harness, parser=parser, jdk_default=get_default_jdk())
 
 def junit_simple(args):
-    return junit(['--tests', _simple_unit_tests()] + args)
+    return mx.command_function('junit')(['--tests', _simple_unit_tests()] + args)
 
 def junit_noapps(args):
-    return junit(['--tests', _gate_noapps_unit_tests()] + args)
+    return mx.command_function('junit')(['--tests', _gate_noapps_unit_tests()] + args)
 
 def junit_nopkgs(args):
-    return junit(['--tests', ','.join([_simple_unit_tests(), _nodes_unit_tests()])] + args)
+    return mx.command_function('junit')(['--tests', ','.join([_simple_unit_tests(), _nodes_unit_tests()])] + args)
 
 def junit_default(args):
-    return junit(['--tests', _all_unit_tests()] + args)
+    return mx.command_function('junit')(['--tests', _all_unit_tests()] + args)
 
 def junit_gate(args):
-    return junit(['--tests', _gate_unit_tests()] + args)
+    return mx.command_function('junit')(['--tests', _gate_unit_tests()] + args)
 
 def _test_package():
     return 'com.oracle.truffle.r.test'