Why are the python reasons for having our code nested in a directory
called ``swift_build_support.swift_build_support/`` instead of simply
``swift_build_support/``? Is that what we really want here?
* swift_build_support: do not raise exception when capturing shell with optional flag
This fixes one of https://bugs.swift.org/browse/SR-2966 failed tests when testing environment trying to instantiate FreeBSD toolchain on Linux and `sysctl` is not in the PATH
* swift_build_support: fix shell test
Under certain obscure circumstances (incomplete SDKs), xcodebuild can
successfully work with the SDK and print its version number, but will
still exit with a non-zero code. This change works around the issue by
ignoring the exit code.
