fix build script array expansion
fix build script array expansion

Summary:
this is the most portable way according to:
https://gist.github.com/dimo414/2fb052d230654cc0c25e9e41a9651ebe

fixed #143

Reviewed By: avasylev

Differential Revision: D23013599

fbshipit-source-id: 5d766e9f4ab5cc6cdc3311a5dbd745f23a5854b8

facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst