[TestPluginCommands] Add skipIfGcc at the right place.

[sivachandra]

Summary

The decorator @expectedFailureGcc was at the wrong place skipping this
test all together. This patch removes it and adds skipIfGcc at the right
place.

[chaoren]

LGTM, I'll look into the crash, and change it to xfail if I can fix it.

test/functionalities/plugins/commands/TestPluginCommands.py

 """
 Test that plugins that load commands work correctly.
 """
 
 import os, time
 import re
 import unittest2
 import lldb
 from lldbtest import *
 import lldbutil
 
-@expectedFailureGcc #xfail to get buildbot green, test failed with gcc4.8.2
 class PluginCommandTestCase(TestBase):
 
     mydir = TestBase.compute_mydir(__file__)
 
     def setUp(self):
         # Call super's setUp().
         TestBase.setUp(self)
         self.lib_dir = os.environ["LLDB_LIB_DIR"]
         self.implib_dir = os.environ["LLDB_IMPLIB_DIR"]
 
     @expectedFailureFreeBSD('llvm.org/pr17430')
     @skipIfi386 # This test links against liblldb.so. Thus, the test requires a 32-bit liblldb.so.
+    @skipIfGcc # llvm.org/pr23221
     @skipIfNoSBHeaders
     def test_load_plugin(self):
         """Test that plugins that load commands work correctly."""
 
         plugin_name = "plugin"
         if sys.platform.startswith("darwin"):
             plugin_lib_name = "lib%s.dylib" % plugin_name
         else: