Added support for building for tvOS

This change is just to add support for building for tvOS.
It is exactly the same as iOS, just using a different SDK.

I had to change the two lines for libjpeg-turbo so that
it will run for both tvOS and iOS.

BUG=skia:

Change-Id: I6ae5fc4257df74c0f321e5d2d71584f6a52ec3a6
Reviewed-on: https://skia-review.googlesource.com/9660
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
diff --git a/gn/BUILD.gn b/gn/BUILD.gn
index 7741354..36c881c 100644
--- a/gn/BUILD.gn
+++ b/gn/BUILD.gn
@@ -50,9 +50,16 @@
 }
 
 if (is_ios) {
-  sdk = "iphoneos"
-  if (target_cpu == "x86" || target_cpu == "x64") {
-    sdk = "iphonesimulator"
+  if (is_tvos) {
+    sdk = "appletvos"
+    if (target_cpu == "x86" || target_cpu == "x64") {
+      sdk = "appletvsimulator"
+    }
+  } else {
+    sdk = "iphoneos"
+    if (target_cpu == "x86" || target_cpu == "x64") {
+      sdk = "iphonesimulator"
+    }
   }
   ios_sysroot = exec_script("find_ios_sysroot.py", [ sdk ], "trim string")
 }