feat: Add proper support for IBM i

Python 3.9 on IBM i now properly returns "os400" for sys.platform
instead of claiming to be AIX as it did previously. While the IBM i PASE
environment is compatible with AIX, it is a subset and has numerous
differences which makes it beneficial to distinguish, however this means
that it now needs explicit support here.

addon.gypi

@@ -103,6 +103,11 @@
           '-Wl,-bimport:<(node_exp_file)'
         ],
       }],
+      [ 'OS=="os400"', {
+        'ldflags': [
+          '-Wl,-bimport:<(node_exp_file)'
+        ],
+      }],
       [ 'OS=="zos"', {
         'cflags': [
           '-q64',

lib/build.js

@@ -11,6 +11,8 @@ function build (gyp, argv, callback) {
   var platformMake = 'make'
   if (process.platform === 'aix') {
     platformMake = 'gmake'
+  } else if (process.platform === 'os400') {
+    platformMake = 'gmake'
   } else if (process.platform.indexOf('bsd') !== -1) {
     platformMake = 'gmake'
   } else if (win && argv.length > 0) {

lib/configure.js

@@ -176,12 +176,12 @@ function configure (gyp, argv, callback) {
     // For AIX and z/OS we need to set up the path to the exports file
     // which contains the symbols needed for linking.
     var nodeExpFile
-    if (process.platform === 'aix' || process.platform === 'os390') {
-      var ext = process.platform === 'aix' ? 'exp' : 'x'
+    if (process.platform === 'aix' || process.platform === 'os390' || process.platform === 'os400') {
+      var ext = process.platform === 'os390' ? 'x' : 'exp'
       var nodeRootDir = findNodeDirectory()
       var candidates
 
-      if (process.platform === 'aix') {
+      if (process.platform === 'aix' || process.platform === 'os400') {
         candidates = [
           'include/node/node',
           'out/Release/node',
@@ -276,7 +276,7 @@ function configure (gyp, argv, callback) {
       argv.push('-Dlibrary=shared_library')
       argv.push('-Dvisibility=default')
       argv.push('-Dnode_root_dir=' + nodeDir)
-      if (process.platform === 'aix' || process.platform === 'os390') {
+      if (process.platform === 'aix' || process.platform === 'os390' || process.platform === 'os400') {
         argv.push('-Dnode_exp_file=' + nodeExpFile)
         if (process.platform === 'os390' && zoslibIncDir) {
           argv.push('-Dzoslib_include_dir=' + zoslibIncDir)

test/test-find-node-directory.js

@@ -4,7 +4,7 @@ const test = require('tap').test
 const path = require('path')
 const findNodeDirectory = require('../lib/find-node-directory')
 
-const platforms = ['darwin', 'freebsd', 'linux', 'sunos', 'win32', 'aix']
+const platforms = ['darwin', 'freebsd', 'linux', 'sunos', 'win32', 'aix', 'os400']
 
 // we should find the directory based on the directory
 // the script is running in and it should match the layout