swift234

Revert "Error out on invalid LLDB build configurations on OS X."

This reverts commit b08610bc3e4acfc2842349e4e661a38b93d4dd27.

The check for LLDB build variant really needs to happen in
build-script-impl.  build-script can still take options after
the '--' separator that may control the final determination
of the LLDB build variant.  These weren't all being considered
by the logic in build-script.