swift

f88212f4 - [Build] Stop CMake from de-duplicating -Xfrontend options.

[Build] Stop CMake from de-duplicating -Xfrontend options. CMake has a misfeature wherein it tries to de-duplicate command line options. This caused it to omit an `-Xfrontend` option when using `add_pure_swift_host_library`. rdar://106547267