Commit 3d14f036199d added the possibility to use `VPP_BUILD_USER` and
`VPP_BUILD_HOST` from environment (if they are set) to avoid
reproducibility issues by hard-coding such data in the build system.
However, there's no way to provide VPP_BUILD_TOPDIR externally. Add this
feature to improve binary reproducibility.
Type: improvement
Change-Id: I3a7ee47d75af9635b636fa3750a3688314eaa60d
Signed-off-by: Oleksandr Hnatiuk <ohnatiuk@cisco.com>
20956385c7