Add decorator for intermittently failing test on FreeBSD

This test has intermittently failed on FreeBSD for quite some time when
run as part of the full test suite.  It generally passes when run by
itself.  Mark as expected failure for now to reduce buildbot noise.

llvm.org/pr15039 test fails intermittently on FreeBSD

llvm-svn: 222134

lldb/test/python_api/value/change_values/TestChangeValueAPI.py

@@ -42,6 +42,7 @@ class ChangeValueAPITestCase(TestBase):
         self.end_line = line_number ('main.c', '// Set a breakpoint here at the end')
 
     @skipIfGcc # llvm.org/pr15039: If GCC is the test compiler, stdout is not available via lldb.SBProcess.GetSTDOUT()
+    @expectedFailureFreeBSD("llvm.org/pr15039 test fails intermittently on FreeBSD")
     def change_value_api(self, exe_name):
         """Exercise some SBValue APIs."""
         exe = os.path.join(os.getcwd(), exe_name)