This won't affect device tests on the bots (because those already set LLVM
manually when testing Release), but it becomes less confusing when trying to
reproduce any problems locally, since now the project configuration on disk
matches the tested configuration.
Exclude tests whose category is !BITCODE when running on watchOS/Release. This
also requires a minor update to xharness to add a BITCODE conditional
compilation flag to generated watchOS/Release projects configurations.
This partially fixes#59947 (the fix will be complete once we bump to mono/2017-08).
https://bugzilla.xamarin.com/show_bug.cgi?id=59947