This renames the package+symbols in the earlier 17ffa80138 to be
in their own package ("buildfeatures") and start with the word "Has"
like "if buildfeatures.HasFoo {".
Updates #12614
Change-Id: I510e5f65993e5b76a0e163e3aa4543755213cbf6
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
So code (in upcoming PRs) can test for the build tags with consts and
get dead code elimination from the compiler+linker.
Updates #12614
Change-Id: If6160453ffd01b798f09894141e7631a93385941
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Brad Fitzpatrick