[debuginfo-tests][Dexter] Fix some Windows-unfriendly Dexter behaviours

[jmorse]

Summary

These are some minor things that I've run into on Windows, largely in error handling paths:

• Giving --lldb-executable on Windows triggers a "useless option" code path, which touches an attribute that only exists in the list_debuggers tool. Switch this to use hasattr, which will work in all subtools.
• We were over-decoding some text reporting errors, but only in an exception path
• The path to lldb on Windows needs to be quoted (even though dexter isn't making use of it).

[Orlando]

LGTM

debuginfo-tests/dexter/dex/debugger/Debuggers.py

return {
         DbgEng.get_option_name(): DbgEng,
         LLDB.get_option_name(): LLDB,
         VisualStudio2015.get_option_name(): VisualStudio2015,
         VisualStudio2017.get_option_name(): VisualStudio2017
     }
 
 
 def _warn_meaningless_option(context, option):
-    if context.options.list_debuggers:
+    if hasattr(context.options, 'list_debuggers'):
         return
 
     warn(context,
          'option <y>"{}"</> is meaningless with this debugger'.format(option),
          '--debugger={}'.format(context.options.debugger))
 
 
 def add_debugger_tool_base_arguments(parser, defaults):

debuginfo-tests/dexter/dex/tools/test/Tool.py

class TestCase(object):
     def __str__(self):
         if self.error and self.context.options.verbose:
             verbose_error = str(self.error)
         else:
             verbose_error = ''
 
         if self.error:
             script_error = (' : {}'.format(
-                self.error.script_error.splitlines()[0].decode()) if getattr(
+                self.error.script_error.splitlines()[0]) if getattr(
                     self.error, 'script_error', None) else '')
 
             error = ' [{}{}]'.format(
                 str(self.error).splitlines()[0], script_error)
         else:
             error = ''
 
         try:

debuginfo-tests/lit.cfg.py

if lldb_path is not None:
     config.available_features.add('lldb')
 
 # Produce dexter path, lldb path, and combine into the %dexter substitution
 # for running a test.
 dexter_path = os.path.join(config.debuginfo_tests_src_root,
                            'dexter', 'dexter.py')
 dexter_test_cmd = '"{}" "{}" test'.format(config.python3_executable, dexter_path)
 if lldb_path is not None:
-  dexter_test_cmd += ' --lldb-executable {}'.format(lldb_path)
+  dexter_test_cmd += ' --lldb-executable "{}"'.format(lldb_path)
 tools.append(ToolSubst('%dexter', dexter_test_cmd))
 
 # For testing other bits of dexter that aren't under the "test" subcommand,
 # have a %dexter_base substitution.
 dexter_base_cmd = '"{}" "{}"'.format(config.python3_executable, dexter_path)
 tools.append(ToolSubst('%dexter_base', dexter_base_cmd))
 
 tool_dirs = [config.llvm_tools_dir]