have the __FBSDID() macro in <sys/cdefs.h>. Fix this once and for all
for tools that need to be bootstrapped.
PR: bin/36747
MFC after: 3 days
Prodded by: obrien
to avoid polluting sys.mk. This directive controls the addition of
compiler warning flags to CFLAGS in a relatively compiler-neutral manner.
The idea is that WARNS can be set in Makefile.inc or in individual
Makefiles as they become clean, to prevent the introduction of new
warnings in the code. -Werror is added by default
