stans: Narrow the scope of includes and other flags

CFLAGS+= here affects *ALL* libsa files being built. However, this is
only needed for zfs.c, so define it only for this. Also, use the defines
from defs.mk. Move all the zfs.c include hacks together. Also, move the
-Wformat -Wall warnings that were added to CFLAGS+= to the individual
files instead for the same reason.

Sponsored by:		Netflix

stand/libsa/zfs/Makefile.inc

@@ -30,6 +30,7 @@ ZFS_EARLY=	-I${ZFSOSINC}					\
 
 .for i in ${ZFS_SRC} ${ZSTD_SRC}
 CFLAGS.$i+=	-include ${ZFSOSINC}/spl/sys/ccompile.h
+CFLAGS.$i+=	-Wformat -Wall
 .endfor
 
 CFLAGS_EARLY.list.c+= ${ZFS_EARLY}
@@ -39,7 +40,9 @@ CFLAGS_EARLY.zstd_shim.c+= ${ZFS_EARLY}
 # the zfs code that need to be unified.
 CFLAGS.nvlist.c+= -I${ZFSOSINC}/spl
 CFLAGS.zfs.c+=	-I${ZFSOSINC}/spl 				\
-		-I${SRCTOP}/sys/cddl/contrib/opensolaris/common/lz4
+		-I${SRCTOP}/sys/cddl/contrib/opensolaris/common/lz4 \
+		-I${ZFSOSINC}/zfs				\
+		-I${OZFS}/include
 
 #
 # ZSTD coding style has some issues, so suppress clang's warnings. Also, zstd's
@@ -53,9 +56,3 @@ CFLAGS.zstd_shim.c+= -DIN_BASE -DIN_LIBSA -I${OZFS}/include
 
 # Do not unroll skein loops, reduce code size
 CFLAGS.skein_block.c+=	-DSKEIN_LOOP=111
-
-CFLAGS+=	-I${SYSDIR}/contrib/openzfs/include
-CFLAGS+=	-I${SYSDIR}/contrib/openzfs/include/os/freebsd/zfs
-CFLAGS.zfs.c+=	-I${SYSDIR}/cddl/contrib/opensolaris/common/lz4
-
-CFLAGS+=	-Wformat -Wall