csu: add crtbrand.o dependency on sys/param.h

FreeBSD_version is recorded in *crt1.o and crti.o via crtbrand.o. Add
an explicit dependency to pick up FreeBSD_version bumps.

Additional changes are required to fully plumb *crt1.o dependencies
through the build.

Reported by: bapt
Reviewed by: bapt
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D43417

(cherry picked from commit ed3563b0ac31d854bf907d4d847ac0195ec9637b)
(cherry picked from commit 090674a3dbf88956f097a3f7e8d9ca1b33aee4ad)