Use `get_build_target` consistently (#2857)
Use `get_build_target` consistently (#2857)

There were still a few places in the bootstrap script that were using a
hardcoded target triple.

rdar://problem/63036398
apple/swift-package-manager,abertelrud/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,abertelrud/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager