Add AppleTV to xplat targets part 2

Summary: More xplat targets need AppleTV SDK support.

Reviewed By: mzlee

Differential Revision: D91059066

fbshipit-source-id: 729271c53cf40aa99559c38e3a8547b41f15d8b4

Author: sbuggay

folly/defs.bzl

@@ -8,6 +8,7 @@ load(
     "@fbsource//tools/build_defs:default_platform_defs.bzl",
     "ANDROID",
     "APPLE",
+    "APPLETVOS",
     "CXX",
     "FBCODE",
     "IOS",
@@ -107,7 +108,7 @@ WINDOWS_CLANG_CXX_FLAGS = [
     "-D_ENABLE_EXTENDED_ALIGNED_STORAGE",
 ]
 
-DEFAULT_APPLE_SDKS = (IOS, MACOSX)
+DEFAULT_APPLE_SDKS = (IOS, APPLETVOS, MACOSX)
 DEFAULT_PLATFORMS = (CXX, ANDROID, APPLE, FBCODE, WINDOWS)
 
 def _compute_include_directories():