Fix fuchsia build of libfeature_support.

This enables the linux path for GetSystemInfo on fuchsia. Tested
locally and fixes the build.

Bug: angleproject:2996
Change-Id: Icc8f282a66ff43ae9c74545a9dcee2d4af8a21e0
Reviewed-on: https://chromium-review.googlesource.com/c/1358632
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>

BUILD.gn

@@ -284,7 +284,7 @@ static_library("angle_gpu_info_util") {
     defines += [ "GPU_INFO_USE_SETUPAPI" ]
   }
 
-  if (is_linux) {
+  if (is_linux || is_fuchsia) {
     sources += libangle_gpu_info_util_linux_sources
 
     if (use_x11) {