build: add node_module_version to config.gypi

Enable targetting of a different node version than
the currently running one when building binary modules.

Based on nodejs/node@410296c37

PR-URL: nodejs#8027
Ref: nodejs#7808
Ref: nodejs/node-gyp#855

configure

@@ -594,6 +594,8 @@ def configure_node(o):
   if options.v8_options:
     o['variables']['node_v8_options'] = options.v8_options.replace('"', '\\"')
 
+  o['variables']['node_module_version'] = 14
+
 
 def configure_libz(o):
   o['variables']['node_shared_zlib'] = b(options.shared_zlib)

node.gyp

@@ -14,6 +14,7 @@
     'node_shared_openssl%': 'false',
     'node_use_mdb%': 'false',
     'node_v8_options%': '',
+    'node_module_version%': '',
     'library_files': [
       'src/node.js',
       'lib/_debugger.js',

test/simple/test-module-version.js

@@ -0,0 +1,10 @@
+'use strict';
+require('../common');
+var assert = require('assert');
+
+// Check for existence
+assert(process.config.variables.hasOwnProperty('node_module_version'));
+
+// Ensure that `node_module_version` is an Integer
+assert(!Number.isNaN(parseInt(process.config.variables.node_module_version)));
+assert.strictEqual(process.config.variables.node_module_version, 14);