build lua tools

It'd be nice to not have them bitrot.

Lua tries to use system(), which doesn't work on iOS.

Change-Id: Ib4370e8703accaf4675f9adfab805f9a7be75852
Reviewed-on: https://skia-review.googlesource.com/92220
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
diff --git a/BUILD.gn b/BUILD.gn
index 1ca9b44..64792d2 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -25,7 +25,7 @@
   skia_use_libjpeg_turbo = true
   skia_use_libpng = true
   skia_use_libwebp = !is_fuchsia
-  skia_use_lua = false
+  skia_use_lua = is_skia_dev_build && !is_ios
   skia_use_piex = !is_win
   skia_use_zlib = true
   skia_use_metal = false