Fix "win-asan-test" random failures and timeouts While exact reason for the failures is unknown, it seems like disabling Vulkan Loader DLL unloading fixes the problem. More details in the issue 8347. This CL also sets the variable on the Linux platform, because it does not hurt and will probably help with similar issues. Bug: angleproject:8347 Change-Id: I398d55a7c13f1ce6790988983fdf8fee7cc5776c Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4868220 Commit-Queue: Igor Nazarov <i.nazarov@samsung.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>