Add test for build script being run multiple times.
Add test for build script being run multiple times.

rust-lang/cargo,vojtechkral/cargo,tshepang/cargo,rustyhorde/cargo,rust-lang/cargo,eminence/cargo,vojtechkral/cargo,rustyhorde/cargo,tshepang/cargo,rust-lang/cargo,rustyhorde/cargo,tshepang/cargo,tsurai/cargo,rustyhorde/cargo,nipunn1313/cargo,tsurai/cargo,nipunn1313/cargo,nipunn1313/cargo,tsurai/cargo,tsurai/cargo,vojtechkral/cargo,rust-lang/cargo,tshepang/cargo,nipunn1313/cargo,eminence/cargo,tsurai/cargo,eminence/cargo,eminence/cargo,vojtechkral/cargo