vboot: add weak __attribute__ tag to stub functions

Function stubs in vboot2 namespace are all marked with
__attribute__((weak)) tags, whereas those in vboot1
are not.  Add the tag to stubs in vboot1 for consistency.

BUG=b:124141368, chromium:968464
TEST=make clean && make runtests

Signed-off-by: Joel Kitching <kitching@google.com>
Change-Id: I8e54ef82882bd80720f810c17f41e902af244ead
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2635673
Tested-by: Joel Kitching <kitching@chromium.org>
Reviewed-by: Yu-Ping Wu <yupingso@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
4 files changed