newvers: Add a builddir parameter

[markj]

Summary

When reproducible builds are configured, we should use /usr/obj as the
canonical objdir. Add a parameter to newvers.sh to ensure that build
metadata is reproducible.

[emaste]

I believe this one is generally not necessary in practice, as in reproducible build mode we already elide the objdir entirely.

[markj]

In D50954#1171688, @emaste wrote:

I believe this one is generally not necessary in practice, as in reproducible build mode we already elide the objdir entirely.

Note that d, derived from $(pwd), is embedded directly into VERSTR. Without this change, when running uname -v, you'll see the value of $(pwd) embedded in the kernel build directory.