Don't override SDKs passed in via explicit compiler arguments.
Don't override SDKs passed in via explicit compiler arguments.

Normally when debugging we work pretty hard to find a compatible SDK.  But if
someone has already told us (via the extra_options flags for
GetScratchSwiftASTContext) then we should respect that and not try to second
guess them.

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb