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

lib/csu/Makefile.inc

@@ -55,6 +55,9 @@ Scrt1_c.o: ${CRT1SRC}
 Scrt1.o: Scrt1_c.o ${CRT1OBJS} ${CRT1OBJ}
 	${LD} ${_LDFLAGS} -o ${.TARGET} -r ${.ALLSRC:M*.o}
 
+# __FreeBSD_version is recorded in crt1.o et al via crtbrand.
+crtbrand.o: ${SRCTOP}/sys/sys/param.h
+
 crtbegin.o: crtbegin.c
 crtbeginS.o: crtbegin.c
 crtbeginT.o: crtbegin.c