[dsymutil] Filter our swiftinterface files from the toolchain. (#71205)

Dsymutil already avoids copying textual Swift interface files from the
SDK, since any consumer would have to have a matching SDK installed
anyway. It should also do the same thing with interfaces found in the
toolchain itself, which includes the compiler built-in libraries such as
Swift (=the standard library), and _Concurrency.

rdar://117881604