openzfs: fix gcc kernel module builds

 - Suppress -Wredundant-decls.  Ultimately this warning is harmless in
   any case, and it does not look like there is a simple way to avoid
   redundant declarations in this case without a lot of header pollution
   (e.g. having openzfs's shim param.h pulling in sys/kernel.h for hz).
 - Suppress -Wnested-externs, which is useless anyway.

Unfortunately it was not sufficient just to modify OPENZFS_CFLAGS,
because the warning suppressions need to appear on the command line
after they are explicitly enabled by CWARNFLAGS from sys/conf/kern.mk,
but OPENZFS_CFLAGS get added before due to use of -I for the shims.

Reviewed by:	markj
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D27685

16 files changed, 18 insertions, 1 deletions

diff --git a/sys/conf/kmod.mk b/sys/conf/kmod.mk
index 54ecbdf69c88..dcc00829b831 100644
--- a/sys/conf/kmod.mk
+++ b/sys/conf/kmod.mk
@@ -540,7 +540,9 @@ OPENZFS_CFLAGS=     \
 	-I${SYSDIR}/cddl/compat/opensolaris \
 	-I${SYSDIR}/cddl/contrib/opensolaris/uts/common \
 	-include ${ZINCDIR}/os/freebsd/spl/sys/ccompile.h
-
+OPENZFS_CWARNFLAGS= \
+	-Wno-nested-externs \
+	-Wno-redundant-decls
 
 .include <bsd.dep.mk>
 .include <bsd.clang-analyze.mk>
diff --git a/sys/modules/dtrace/dtaudit/Makefile b/sys/modules/dtrace/dtaudit/Makefile
index 72cdf03f4bc3..3571bcbb7ea2 100644
--- a/sys/modules/dtrace/dtaudit/Makefile
+++ b/sys/modules/dtrace/dtaudit/Makefile
@@ -13,3 +13,4 @@ CFLAGS+= ${OPENZFS_CFLAGS}
 .include <bsd.kmod.mk>
 
 CFLAGS+=	-include ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
+CWARNFLAGS+=	${OPENZFS_CWARNFLAGS}
diff --git a/sys/modules/dtrace/dtmalloc/Makefile b/sys/modules/dtrace/dtmalloc/Makefile
index 910f8f360e80..ffde4f811ee8 100644
--- a/sys/modules/dtrace/dtmalloc/Makefile
+++ b/sys/modules/dtrace/dtmalloc/Makefile
@@ -13,3 +13,4 @@ CFLAGS+=	${OPENZFS_CFLAGS}
 .include <bsd.kmod.mk>
 
 CFLAGS+=	-include ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
+CWARNFLAGS+=	${OPENZFS_CWARNFLAGS}
diff --git a/sys/modules/dtrace/dtnfscl/Makefile b/sys/modules/dtrace/dtnfscl/Makefile
index 6184ad183fc6..d28641e51ec8 100644
--- a/sys/modules/dtrace/dtnfscl/Makefile
+++ b/sys/modules/dtrace/dtnfscl/Makefile
@@ -13,3 +13,4 @@ CFLAGS+=	${OPENZFS_CFLAGS}
 .include <bsd.kmod.mk>
 
 CFLAGS+=	-include ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
+CWARNFLAGS+=	${OPENZFS_CWARNFLAGS}
diff --git a/sys/modules/dtrace/dtrace/Makefile b/sys/modules/dtrace/dtrace/Makefile
index 0bedcaa12fe7..80278fc83a32 100644
--- a/sys/modules/dtrace/dtrace/Makefile
+++ b/sys/modules/dtrace/dtrace/Makefile
@@ -59,6 +59,7 @@ dtrace_asm.o:  assym.inc
 
 CFLAGS+=	-include ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
 CFLAGS.dtrace_asm.S+= -D_SYS_ERRNO_H_ -D_SYS_PARAM_H_ -DLOCORE
+CWARNFLAGS+=	${OPENZFS_CWARNFLAGS}
 CWARNFLAGS+=	-Wno-parentheses
 CWARNFLAGS+=	-Wno-uninitialized
 CWARNFLAGS+=	-Wno-cast-qual
diff --git a/sys/modules/dtrace/fasttrap/Makefile b/sys/modules/dtrace/fasttrap/Makefile
index 1be1b97736ea..0eecfcb11aab 100644
--- a/sys/modules/dtrace/fasttrap/Makefile
+++ b/sys/modules/dtrace/fasttrap/Makefile
@@ -26,5 +26,6 @@ SRCS+=		u8_textprep.c
 
 CFLAGS+=	-include ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
 
+CWARNFLAGS+=	${OPENZFS_CWARNFLAGS}
 CWARNFLAGS+=	-Wno-cast-qual
 CWARNFLAGS+=	-Wno-unused
diff --git a/sys/modules/dtrace/fbt/Makefile b/sys/modules/dtrace/fbt/Makefile
index 288c8cafa817..360d92000776 100644
--- a/sys/modules/dtrace/fbt/Makefile
+++ b/sys/modules/dtrace/fbt/Makefile
@@ -23,3 +23,4 @@ CFLAGS+=  -I${SYSDIR}/cddl/dev/fbt
 .include <bsd.kmod.mk>
 
 CFLAGS+=	-include ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
+CWARNFLAGS+=	${OPENZFS_CWARNFLAGS}
diff --git a/sys/modules/dtrace/profile/Makefile b/sys/modules/dtrace/profile/Makefile
index aa36f9a2dfba..b3eec9a19f23 100644
--- a/sys/modules/dtrace/profile/Makefile
+++ b/sys/modules/dtrace/profile/Makefile
@@ -13,3 +13,4 @@ CFLAGS+= 	${OPENZFS_CFLAGS}
 .include <bsd.kmod.mk>
 
 CFLAGS+=	-include ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
+CWARNFLAGS+=	${OPENZFS_CWARNFLAGS}
diff --git a/sys/modules/dtrace/prototype/Makefile b/sys/modules/dtrace/prototype/Makefile
index 476c567a4dc0..189d6c2df2a2 100644
--- a/sys/modules/dtrace/prototype/Makefile
+++ b/sys/modules/dtrace/prototype/Makefile
@@ -13,3 +13,4 @@ CFLAGS+= 	${OPENZFS_CFLAGS}
 .include <bsd.kmod.mk>
 
 CFLAGS+=	-include ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
+CWARNFLAGS+=	${OPENZFS_CWARNFLAGS}
diff --git a/sys/modules/dtrace/sdt/Makefile b/sys/modules/dtrace/sdt/Makefile
index 2f6432e4a71f..a025848e3a60 100644
--- a/sys/modules/dtrace/sdt/Makefile
+++ b/sys/modules/dtrace/sdt/Makefile
@@ -12,3 +12,4 @@ CFLAGS+=	${OPENZFS_CFLAGS}
 
 .include <bsd.kmod.mk>
 CFLAGS+=	-include ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
+CWARNFLAGS+=	${OPENZFS_CWARNFLAGS}
diff --git a/sys/modules/dtrace/systrace/Makefile b/sys/modules/dtrace/systrace/Makefile
index 3e122f70da25..2250a7418193 100644
--- a/sys/modules/dtrace/systrace/Makefile
+++ b/sys/modules/dtrace/systrace/Makefile
@@ -13,3 +13,4 @@ CFLAGS+=	${OPENZFS_CFLAGS}
 .include <bsd.kmod.mk>
 
 CFLAGS+=	-include ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
+CWARNFLAGS+=	${OPENZFS_CWARNFLAGS}
diff --git a/sys/modules/dtrace/systrace_freebsd32/Makefile b/sys/modules/dtrace/systrace_freebsd32/Makefile
index 4661633f9a62..3b77bc4c6d0e 100644
--- a/sys/modules/dtrace/systrace_freebsd32/Makefile
+++ b/sys/modules/dtrace/systrace_freebsd32/Makefile
@@ -14,3 +14,4 @@ CFLAGS+=	-DFREEBSD32_SYSTRACE
 .include <bsd.kmod.mk>
 
 CFLAGS+=	-include ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
+CWARNFLAGS+=	${OPENZFS_CWARNFLAGS}
diff --git a/sys/modules/dtrace/systrace_linux/Makefile b/sys/modules/dtrace/systrace_linux/Makefile
index 7dbd88ffb5f0..56f422dfb9e5 100644
--- a/sys/modules/dtrace/systrace_linux/Makefile
+++ b/sys/modules/dtrace/systrace_linux/Makefile
@@ -15,3 +15,4 @@ CFLAGS+=	-DLINUX_SYSTRACE
 .include <bsd.kmod.mk>
 
 CFLAGS+=	-include ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
+CWARNFLAGS+=	${OPENZFS_CWARNFLAGS}
diff --git a/sys/modules/dtrace/systrace_linux32/Makefile b/sys/modules/dtrace/systrace_linux32/Makefile
index 81aa1b7de9df..febd4a0c1bab 100644
--- a/sys/modules/dtrace/systrace_linux32/Makefile
+++ b/sys/modules/dtrace/systrace_linux32/Makefile
@@ -15,3 +15,4 @@ CFLAGS+=	-DLINUX32_SYSTRACE
 .include <bsd.kmod.mk>
 
 CFLAGS+=	-include ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
+CWARNFLAGS+=	${OPENZFS_CWARNFLAGS}
diff --git a/sys/modules/opensolaris/Makefile b/sys/modules/opensolaris/Makefile
index 1b5dd6dffcfb..536b9637cd3c 100644
--- a/sys/modules/opensolaris/Makefile
+++ b/sys/modules/opensolaris/Makefile
@@ -34,3 +34,4 @@ IGNORE_PRAGMA=	1
 .include <bsd.kmod.mk>
 
 CFLAGS+=	-include ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
+CWARNFLAGS+=	${OPENZFS_CWARNFLAGS}
diff --git a/sys/modules/zfs/Makefile b/sys/modules/zfs/Makefile
index 2318b9b155d3..d2617dc6bdc6 100644
--- a/sys/modules/zfs/Makefile
+++ b/sys/modules/zfs/Makefile
@@ -279,6 +279,7 @@ SRCS+=	zfs_zstd.c \
 
 .include <bsd.kmod.mk>
 
+CWARNFLAGS+=	${OPENZFS_CWARNFLAGS}
 
 CFLAGS.gcc+= -Wno-pointer-to-int-cast