[build-script-migrator] fix TypeError

When running build-script, I get the output below:

    utils/build-script --preset=drew --preset-file=../presets.ini  --preset-file=utils/build-presets.ini installable_package="`pwd`/../osx-caffeinated-$tag.tar.gz" install_destdir="`pwd`/../install" install_symroot="`pwd`/../install_symroot" symbols_package="`pwd`/../osx-caffeinated-symbols-$tag.tar.gz" darwin_toolchain_bundle_identifier="net.caffei.swift.$tag"  darwin_toolchain_display_name="caffeinated-$tag" install_toolchain_dir="/Library/Developer/Toolchains/caffeinated-$tag.xctoolchain"  darwin_toolchain_xctoolchain_name="caffeinated-$tag.xctoolchain" darwin_toolchain_version="caffeinated-$tag" darwin_toolchain_alias="caffeinated-$tag" darwin_toolchain_display_name_short="caffeinated-$tag"
    utils/build-script: using preset 'drew', which expands to utils/build-script --ios --tvos --watchos --lldb --llbuild --swiftpm --release-debuginfo --build-subdir=buildbot_osx --ios --tvos --watchos --test --validation-test --long-test --assertions --no-swift-stdlib-assertions -- --lldb-no-debugserver --lldb-use-system-debugserver --lldb-build-type=Release --verbose-build --build-ninja --build-swift-static-stdlib --build-swift-stdlib-unittest-extra --compiler-vendor=apple '--swift-sdks=OSX;IOS;IOS_SIMULATOR;TVOS;TVOS_SIMULATOR;WATCHOS;WATCHOS_SIMULATOR' --install-swift --install-lldb --install-llbuild --install-swiftpm --install-destdir=/Users/drew/Code/swift-osx/swift/../install --darwin-install-extract-symbols --install-symroot=/Users/drew/Code/swift-osx/swift/../install_symroot --install-prefix=/Library/Developer/Toolchains/caffeinated-swift-DEVELOPMENT-SNAPSHOT-2016-04-25-a.xctoolchain/usr --test-installable-package --reconfigure --installable-package=/Users/drew/Code/swift-osx/swift/../osx-caffeinated-swift-DEVELOPMENT-SNAPSHOT-2016-04-25-a.tar.gz --swift-enable-ast-verifier=0 '--swift-install-components=compiler;clang-builtin-headers;stdlib;sdk-overlay;license;sourcekit-xpc-service' '--llvm-install-components=libclang;libclang-headers' --installable-package=/Users/drew/Code/swift-osx/swift/../osx-caffeinated-swift-DEVELOPMENT-SNAPSHOT-2016-04-25-a.tar.gz --symbols-package=/Users/drew/Code/swift-osx/swift/../osx-caffeinated-symbols-swift-DEVELOPMENT-SNAPSHOT-2016-04-25-a.tar.gz --darwin-toolchain-bundle-identifier=net.caffei.swift.swift-DEVELOPMENT-SNAPSHOT-2016-04-25-a --darwin-toolchain-display-name=caffeinated-swift-DEVELOPMENT-SNAPSHOT-2016-04-25-a --darwin-toolchain-display-name-short=caffeinated-swift-DEVELOPMENT-SNAPSHOT-2016-04-25-a --darwin-toolchain-name=caffeinated-swift-DEVELOPMENT-SNAPSHOT-2016-04-25-a.xctoolchain --darwin-toolchain-version=caffeinated-swift-DEVELOPMENT-SNAPSHOT-2016-04-25-a --darwin-toolchain-alias=caffeinated-swift-DEVELOPMENT-SNAPSHOT-2016-04-25-a --skip-test-ios --skip-test-tvos --skip-test-watchos
    Traceback (most recent call last):
      File "utils/build-script", line 1339, in <module>
        sys.exit(main())
      File "utils/build-script", line 1335, in main
        return main_normal()
      File "utils/build-script", line 824, in main_normal
        args = migration.parse_args(parser, sys.argv[1:])
      File "utils/swift_build_support/swift_build_support/migration.py", line 34, in parse_args
        arg for arg in argv if arg != '--')
      File "/Library/Python/2.7/site-packages/argparse.py", line 1735, in parse_known_args
        namespace, args = self._parse_known_args(args, namespace)
      File "/Library/Python/2.7/site-packages/argparse.py", line 1941, in _parse_known_args
        start_index = consume_optional(start_index)
      File "/Library/Python/2.7/site-packages/argparse.py", line 1873, in consume_optional
        args = arg_strings[start:stop]
    TypeError: 'generator' object has no attribute '__getitem__'
    utils/build-script: command terminated with a non-zero exit status 1, aborting

This seems to be because the migrator script passes a generator where one was not expected.

Construct a list instead.

Author: drewcrawford

utils/swift_build_support/swift_build_support/migration.py

@@ -31,7 +31,7 @@ def parse_args(parser, argv):
         build-script -RT -- --reconfigure
     """
     args, unknown_args = parser.parse_known_args(
-        arg for arg in argv if arg != '--')
+        list(arg for arg in argv if arg != '--'))
     args.build_script_impl_args = unknown_args
     return args