compile_commands_json breaks on Python3

[gengjiawen]

Similar to #1943

node-gyp configure -- -f compile_commands_json

cc @cclauss

Verbose output (from npm or node-gyp):

gyp info it worked if it ends with ok   
gyp info using node-gyp@6.0.0
gyp info using node@13.0.1 | linux | x64
gyp info find Python using Python version 3.6.8 found at "/usr/bin/python3"
gyp info spawn /usr/bin/python3
gyp info spawn args [
gyp info spawn args   '/usr/local/share/.config/yarn/global/node_modules/node-gyp/gyp/gyp_main.py',     
gyp info spawn args   'binding.gyp',
gyp info spawn args   '-f',
gyp info spawn args   'compile_commands_json',
gyp info spawn args   '-I',
gyp info spawn args   '/mnt/d/Developer/node-addon-examples/2_function_arguments/nan/build/config.gypi',
gyp info spawn args   '-I',
gyp info spawn args   '/usr/local/share/.config/yarn/global/node_modules/node-gyp/addon.gypi',
gyp info spawn args   '-I',
gyp info spawn args   '/home/daniel/.cache/node-gyp/13.0.1/include/node/common.gypi',
gyp info spawn args   '-Dlibrary=shared_library',
gyp info spawn args   '-Dvisibility=default',
gyp info spawn args   '-Dnode_root_dir=/home/daniel/.cache/node-gyp/13.0.1',
gyp info spawn args   '-Dnode_gyp_dir=/usr/local/share/.config/yarn/global/node_modules/node-gyp',      
gyp info spawn args   '-Dnode_lib_file=/home/daniel/.cache/node-gyp/13.0.1/<(target_arch)/node.lib',    
gyp info spawn args   '-Dmodule_root_dir=/mnt/d/Developer/node-addon-examples/2_function_arguments/nan',
gyp info spawn args   '-Dnode_engine=v8',
gyp info spawn args   '--depth=.',
gyp info spawn args   '--no-parallel',
gyp info spawn args   '--generator-output',
gyp info spawn args   'build',
gyp info spawn args   '-Goutput_dir=.'
gyp info spawn args ]
Traceback (most recent call last):
  File "/usr/local/share/.config/yarn/global/node_modules/node-gyp/gyp/gyp_main.py", line 50, in <module>
    sys.exit(gyp.script_main())
  File "/usr/local/share/.config/yarn/global/node_modules/node-gyp/gyp/pylib/gyp/__init__.py", line 554, in script_main
    return main(sys.argv[1:])
  File "/usr/local/share/.config/yarn/global/node_modules/node-gyp/gyp/pylib/gyp/__init__.py", line 547, in main
    return gyp_main(args)
  File "/usr/local/share/.config/yarn/global/node_modules/node-gyp/gyp/pylib/gyp/__init__.py", line 532, in gyp_main
    generator.GenerateOutput(flat_list, targets, data, params)
  File "/usr/local/share/.config/yarn/global/node_modules/node-gyp/gyp/pylib/gyp/generator/compile_commands_json.py", line 95, in GenerateOutput
    for qualified_target, target in target_dicts.iteritems():
AttributeError: 'dict' object has no attribute 'iteritems'
gyp ERR! configure error 
gyp ERR! stack Error: `gyp` failed with exit code: 1
gyp ERR! stack     at ChildProcess.onCpExit (/usr/local/share/.config/yarn/global/node_modules/node-gyp/lib/configure.js:351:16)
gyp ERR! stack     at ChildProcess.emit (events.js:210:5)
gyp ERR! stack     at Process.ChildProcess._handle.onexit (internal/child_process.js:272:12)
gyp ERR! System Linux 4.4.0-18362-Microsoft
gyp ERR! command "/usr/local/bin/node" "/usr/local/bin/node-gyp" "configure" "--" "-f" "compile_commands_json"
gyp ERR! cwd /mnt/d/Developer/node-addon-examples/2_function_arguments/nan
gyp ERR! node -v v13.0.1
gyp ERR! node-gyp -v v6.0.0
gyp ERR! not ok

[bnoordhuis]

Closing as #1947 was merged.