Vulkan's cmake files check for the availability of secure_getenv() but we
just assume it exists.

BUG=chromium:717558

Change-Id: I22054c3967f543d163dde37b9a6b13e896da7a50
Reviewed-on: https://chromium-review.googlesource.com/494126
Commit-Queue: Frank Henigman <fjhenigman@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>