Fix Fuchsia Vulkan build control

Our last patch here ran into some problems because some people build a
subset of fuchsia that does not include skia, so setting skia_use_vulkan
breaks their build. This relies on buildargs set from a fuchsia global
GNI file to allow us to set them independently of skia in our build
system

Change-Id: I64f5f0f349c12947c8aff7761dc5fafdb6a91b6c
Reviewed-on: https://skia-review.googlesource.com/13617
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Greg Daniel <egdaniel@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
1 file changed