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/1358632Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>