dh: Use minimal sequences if delegating work

dh: Use minimal sequences if delegating work

The build and install rules run a minimal sequence if the build-arch or
build-indep, or install-arch or install-indep targets, respectively,
are present in debian/rules.  The purpose is to not do work ahead of
time, such as building before the build-arch or build-indep targets are
built, which could potentially lead to misbuilds.  If the targets are
not defined, the sequences may be run directly which is faster due to
being able to run the arch and indep commands together.