vboot: Add mockable attribute to some overridden functions

A newer clang version has an optimization that is breaking
vboot_reference unit tests. The root cause appears to be:
Many functions inside unit tests are supposed to override
the functions defined in the main library but the main
library functions are not defined as weak.

Fix by marking some of the overridden function by
test_mockable which is already used for some of the functions.

This is similar to a prior bug 723906 where unit tests
were broken after binutils upgrade.

BUG=chromium:1055151
TEST=unit tests passed with ToT clang

Change-Id: Ib9f16e1af59632b6a82411656ebba75e26b5d211
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2069806
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Joel Kitching <kitching@chromium.org>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
6 files changed