Add a flag BI_BRAND_ONLY_STATIC to specify that the brand only

Add a flag BI_BRAND_ONLY_STATIC to specify that the brand only
matches static binaries.

Interpretation of the 'static' there is that the binary must not
specify an interpreter.  In particular, shared objects are matched by
the brand if BI_CAN_EXEC_DYN is also set.

This improves precision of the brand matching, which should eliminate
surprises due to brand ordering.

Revert r315701.

Discussed with and tested by:	ed (previous version)
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week