build: add support for 64-bit AIX

Pass -Dtarget_arch=ppc64 to gyp_uv.py to activate.

Refs: nodejs/node#20129
Refs: #1795
PR-URL: #1807
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

common.gypi

@@ -134,7 +134,7 @@
           }]
         ]
       }],
-      ['OS in "freebsd dragonflybsd linux openbsd solaris android"', {
+      ['OS in "freebsd dragonflybsd linux openbsd solaris android aix"', {
         'cflags': [ '-Wall' ],
         'cflags_cc': [ '-fno-rtti', '-fno-exceptions' ],
         'target_conditions': [
@@ -162,6 +162,10 @@
             'cflags': [ '-pthread' ],
             'ldflags': [ '-pthread' ],
           }],
+          [ 'OS=="aix" and target_arch=="ppc64"', {
+            'cflags': [ '-maix64' ],
+            'ldflags': [ '-maix64' ],
+          }],
         ],
       }],
       ['OS=="mac"', {