Change build.conf to default to modular policy builds rather than
monolithic policy builds. Rationale: All modern Linux distributions
that incorporate SELinux support have switched to using modular policy,
and many of the policy tools (semodule, semanage, and even modern
versions of setsebool) only work if using modular policy.
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>