I don't know what worked for you, @drewish, but this is how I got it to work:
{
"targets": [
{
"target_name": "package_name",
'type': 'executable',
'xcode_settings': {
'OTHER_CFLAGS': [
"-std=c++11",
"-stdlib=libc++",
"-mmacosx-version-min=10.7"
],
},
"sources": [ "overcpu.cpp" ],
}
]
}