test: set module loading error for aix

In test/parallel/test-module-loading-error.js, an attempt is made to
load a text file as a native executable. This results in an error
message in a platform specific manner.

AIX was not included in the list of platforms. This fix introduces
the AIX error messages.

PR-URL: #14511
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

test/parallel/test-module-loading-error.js

@@ -8,7 +8,9 @@ const error_desc = {
   win32: ['%1 is not a valid Win32 application'],
   linux: ['file too short', 'Exec format error'],
   sunos: ['unknown file type', 'not an ELF file'],
-  darwin: ['file too short']
+  darwin: ['file too short'],
+  aix: ['Cannot load module',
+        'Cannot run a file that does not have a valid format.']
 };
 const dlerror_msg = error_desc[process.platform];