build: provide a default WARNS for all in-tree builds

The current default is provided in various Makefile.inc in some top-level
directories and covers a good portion of the tree, but doesn't cover parts
of the build a little deeper (e.g. libcasper).

Provide a default in src.sys.mk and set WARNS to it in bsd.sys.mk if that
variable is defined. This lets us relatively cleanly provide a default WARNS
no matter where you're building in the src tree without breaking things
outside of the tree.

Crunchgen has been updated as a bootstrap tool to work on this change
because it needs r365605 at a minimum to succeed. The cleanup necessary to
successfully walk over this change on WITHOUT_CLEAN builds has been added.

There is a supplemental project to this to list all of the warnings that are
encountered when the environment has WARNS=6 NO_WERROR=yes:
https://warns.kevans.dev -- this project will hopefully eventually go away
in favor of CI doing a much better job than it.

Reviewed by:	emaste, brooks, ngie (all earlier version)
Reviewed by:	emaste, arichardson (depend-cleanup.sh change)
Differential Revision:	https://reviews.freebsd.org/D26455

1 files changed, 2 insertions, 0 deletions

diff --git a/rescue/librescue/Makefile b/rescue/librescue/Makefile
index e7147d8e67ce..2116219dc746 100644
--- a/rescue/librescue/Makefile
+++ b/rescue/librescue/Makefile
@@ -23,6 +23,8 @@ INTERNALLIB=	# Don't install this library
 SRCS=		exec.c getusershell.c login_class.c popen.c rcmdsh.c \
 		sysctl.c system.c
 
+WARNS?=		3
+
 CFLAGS+=	-DRESCUE
 # Flags copied from src/lib/libc and src/lib/libutil
 # libc/db/Makefile.inc