#### Why I did it
Mellanox builds were failing intermittently due to the `issue_version` file and MFT package not building correctly in the Azure pipeline environment (both of these packages were patched to build correctly with bullseye running on the host and buster running on the dockers)
#### How I did it
Fixed two problems:
1. BLDENV is not passed to the Makefiles so the references to this were replaced with correct logic
2. `issue_version` was not defined as a target for bullseye and as such was not cached. Altered the build such that it is defined as a target for bullseye (in the case of buster it builds the file, in the case of bullseye it copies from buster)
The previous PR fixing this was reverted as it is no longer necessary for a passing build and was not a long-term fix. https://github.com/Azure/sonic-buildimage/pull/9235
#### How to verify it
Build on AZP and verify success.
The issu-version file for Mellanox is generated from the Mellanox SDK
libraries. The SDK is installed into a Buster docker container, but the
issu-version file goes onto the base OS, which is Bullseye. To work
around this, the issu-version build rules explicitly copies the
issu-version file to target/files/bullseye/ during the Buster build.
Because of our build infra, if caching is enabled and a cache is being
used, then for issu-version, since it is technically built as part of
Buster, then only target/files/buster/issu-version is saved into the
cache, and target/files/bullseye/issu-version isn't cached. If this
cache gets used, then target/files/bullseye/issu-version is missing, and
the final image build fails.
This is to work around the current build issue where Mellanox builds are
failing. This is so that issu-version is always "built", so that copy is
made into the bullseye directory.
Signed-off-by: Saikrishna Arcot <sarcot@microsoft.com>
