shiny/driver: use __MAC_OS_X_VERSION_MAX_ALLOWED for conditional compilation
shiny/driver: use __MAC_OS_X_VERSION_MAX_ALLOWED for conditional compilation

__MAC_OS_X_VERSION_MAX_ALLOWED is official way to do conditional compilation
according to documentation in: https://developer.apple.com/library/content/documentation/DeveloperTools/Conceptual/cross_development/Using/using.html#//apple_ref/doc/uid/20002000-SW5

Fixes golang/go#22634

Change-Id: I916403149ed6a1ede5d8dcb554d152784c302fcb
Reviewed-on: https://go-review.googlesource.com/31546
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/exp,golang/exp,golang/exp