`TargetConditionals.h` was missing several definitions, like
`TARGET_OS_TV` that are part of SDK 10.12 at least. And one that doesn't
seem to occur in any SDK afaict, `TARGET_OS_EMBEDDED_OTHER`.
I added the definitions from SDK 10.12 verbatim and defined
`TARGET_OS_EMBEDDED_OTHER` to be equal to `0`.
This is a modified version of a patch to avoid a stdenv rebuild.