[test] Fix %hmaptool path for standalone builds

[mgorny]

Summary

Fix %hmaptool path to refer to clang_tools_dir instead of
llvm_tools_dir, in order to fix standalone builds. The tool is built
as part of clang, so it won't be found in installed LLVM tools.

[bkramer]

lg, thanks

test/lit.cfg.py

 if config.clang_examples:
     config.available_features.add('examples')
     tools.append('clang-interpreter')
 
 llvm_config.add_tool_substitutions(tools, tool_dirs)
 
 config.substitutions.append(
     ('%hmaptool', "'%s' %s" % (config.python_executable,
-                             os.path.join(config.llvm_tools_dir, 'hmaptool'))))
+                             os.path.join(config.clang_tools_dir, 'hmaptool'))))
 
 # Plugins (loadable modules)
 # TODO: This should be supplied by Makefile or autoconf.
 if sys.platform in ['win32', 'cygwin']:
     has_plugins = config.enable_shared
 else:
     has_plugins = True