Move version out of SDK. For now it's a copy rather than move: the part not addressed by this change is sdk/helper/useragent.String, which we'll want to remove in favour of PluginString. That will have to wait until we've removed uses of useragent.String from all builtins.
Remove gox in favor of go build.
`gox` hasn't had a release to update it in many years, so is missing
support for many modern systems, like `darwin/arm64`.
In any case, we only use it for dev builds, where we don't even use
the ability of it to build for multiple platforms. Release builds use
`go build` now.
So, this switches to `go build` everywhere.
I pulled this down and tested it in Windows as well. (Side note: I
couldn't get `gox` to work in Windows, so couldn't build before this
change.)
* add BuildDate to version base
* populate BuildDate with ldflags
* include BuildDate in FullVersionNumber
* add BuildDate to seal-status and associated status cmd
* extend core/versions entries to include BuildDate
* include BuildDate in version-history API and CLI
* fix version history tests
* fix sys status tests
* fix TestStatusFormat
* remove extraneous LD_FLAGS from build.sh
* add BuildDate to build.bat
* fix TestSysUnseal_Reset
* attempt to add build-date to release builds
* add branch to github build workflow
* add get-build-date to build-* job needs
* fix release build command vars
* add missing quote in release build command
* Revert "add branch to github build workflow"
This reverts commit b835699ecb7c2c632757fa5fe64b3d5f60d2a886.
* add changelog entry
