git: e8e691983bb7 - main - suppress set but not used warnings for kernel builds

The branch main has been updated by rew:

URL: https://cgit.FreeBSD.org/src/commit/?id=e8e691983bb75e80153b802f47733f1531615fa2

commit e8e691983bb75e80153b802f47733f1531615fa2
Author:     Robert Wing <rew@FreeBSD.org>
AuthorDate: 2022-04-05 21:28:54 +0000
Commit:     Robert Wing <rew@FreeBSD.org>
CommitDate: 2022-04-05 21:34:34 +0000

    suppress set but not used warnings for kernel builds
    
    Use -Wno-unused-but-set-variable for kernel builds with clang13.
    
    To turn this warning back on, set the following in src.conf:
        WITH_SET_BUT_NOTUSED_KERNEL_WARNINGS=
    
    Reviewed by:    mjg, imp
    Differential Revision:  https://reviews.freebsd.org/D34784
---
 sys/conf/kern.mk      | 6 +++++-
 sys/conf/kern.opts.mk | 3 ++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/sys/conf/kern.mk b/sys/conf/kern.mk
index f97be774ea10..67756b7fb986 100644
--- a/sys/conf/kern.mk
+++ b/sys/conf/kern.mk
@@ -43,7 +43,11 @@ CWARNEXTRA?=	-Wno-error=tautological-compare -Wno-error=empty-body \
 CWARNEXTRA+=	-Wno-error=shift-negative-value
 CWARNEXTRA+=	-Wno-address-of-packed-member
 .if ${COMPILER_VERSION} >= 130000
-CWARNFLAGS+=	-Wno-error=unused-but-set-variable
+.if ${MK_SET_BUT_NOTUSED_KERNEL_WARNINGS} == "no"
+CWARNEXTRA+=	${NO_WUNUSED_BUT_SET_VARIABLE}
+.else
+CWARNEXTRA+=	-Wno-error=unused-but-set-variable
+.endif
 .endif
 .endif	# clang
 
diff --git a/sys/conf/kern.opts.mk b/sys/conf/kern.opts.mk
index 077009baebf0..19789180ee93 100644
--- a/sys/conf/kern.opts.mk
+++ b/sys/conf/kern.opts.mk
@@ -60,7 +60,8 @@ __DEFAULT_NO_OPTIONS = \
     INIT_ALL_ZERO \
     KERNEL_RETPOLINE \
     RATELIMIT \
-    REPRODUCIBLE_BUILD
+    REPRODUCIBLE_BUILD \
+    SET_BUT_NOTUSED_KERNEL_WARNINGS
 
 # Some options are totally broken on some architectures. We disable
 # them. If you need to enable them on an experimental basis, you