Allow programs to set NO_SHARED on a per-PROG basis

This is particularly useful when installing programs for tests that need to be
linked statically, e.g., mini-me from capsicum-test, which is linked statically
to avoid the dynamic library lookup in the upstream project.

Reviewed by: emaste
Approved by: emaste (mentor)
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D19756