Add support for AIX

For AIX we need to use gmake.

For AIX we need to set up the path to the exp file which contains the
symbols needed for linking.  The file will either be in one of the
following depeding on whether are are in installed or development
environment:

  - the include/node directory
  - the out/Release directory

PR-URL: https://github.com/nodejs/node-gyp/pull/753
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

addon.gypi

@@ -65,6 +65,11 @@
           'DYLIB_INSTALL_NAME_BASE': '@rpath'
         },
       }],
+      [ 'OS=="aix"', {
+        'ldflags': [
+          '-Wl,-bimport:<(node_exp_file)'
+        ],
+      }],
       [ 'OS=="win"', {
         'libraries': [
           '-lkernel32.lib',