Remove -fms-extensions throughout the tree

During a discussion about using -fms-extensions jhb pointed out that
we have them enabled in the kernel for gcc by default (even multiple
times in one part). I had missed all that and clang still failed on
my use case (needing another option).

The original cause for enabling them for our tree back then was that
we needed to support C11 anonymous struct/unions.
Our in-tree gcc 4.2.1, despite later patches, needed the
-fms-extensions to support these even though this was not the expected
use case for that option ( cc4a90c445 enabled it globally for the
kernel).
clang at that time (or at least when it became default for 10.0)
already was fine (with C11).

Any later gcc (4.6.0 onwards) did not need that option anymore, even
when compiled for -std=iso9899:1990 (which does not support anonymous
structs/unions) unless one would add -pedantic (see gcc git 4bdd0a60b27a).
This is also the reason why userland cddl sources now compile with the
option removed despite CSTD=c99.

The only driver which needed the option recently was ccp, but that was
fixed in 8d3f41dbcb by jhb.

So cleanup all uses cases of -fms-extensions for the moment as they are
no longer needed given all compilers currently supported seem to be
fine without them and gcc-4.2.1 was removed from the tree in stable/13
in 2020 (a9854bc381).

Reported by:	jhb (all this but possibly the world CDDL parts)
Sponsored by:	The FreeBSD Foundation
MFC after:	3 days
Reviewed by:	emaste (earlier), imp, jhb, glebius
Differential Revision: https://reviews.freebsd.org/D55072

cddl/lib/libzpool/Makefile

@@ -281,7 +281,6 @@ CFLAGS+=	-DWANTS_MUTEX_OWNED
 CFLAGS+=	-I${SRCTOP}/lib/libpthread/thread
 CFLAGS+=	-I${SRCTOP}/lib/libpthread/sys
 CFLAGS+=	-I${SRCTOP}/lib/libthr/arch/${MACHINE_CPUARCH}/include
-CFLAGS.gcc+=	-fms-extensions
 
 LIBADD=		md pthread z spl icp nvpair avl umem
 

cddl/usr.bin/ztest/Makefile

@@ -28,7 +28,6 @@ CSTD=	c99
 # Since there are many asserts in this program, it makes no sense to compile
 # it without debugging.
 CFLAGS+= -g -DDEBUG=1 -Wno-format -DZFS_DEBUG=1
-CFLAGS.gcc+= -fms-extensions
 
 HAS_TESTS=
 SUBDIR.${MK_TESTS}+= tests

cddl/usr.sbin/zdb/Makefile

@@ -24,7 +24,6 @@ CFLAGS+= \
 
 LIBADD=	nvpair umem zdb zfs_core zfs spl avl zutil zpool crypto pthread
 
-CFLAGS.gcc+= -fms-extensions
 # Since there are many asserts in this program, it makes no sense to compile
 # it without debugging.
 CFLAGS+=	-g -DDEBUG=1 -DZFS_DEBUG=1

sys/conf/kern.pre.mk

@@ -78,10 +78,9 @@ CFLAGS=	${COPTFLAGS} ${DEBUG}
 CFLAGS+= ${INCLUDES} -D_KERNEL -DHAVE_KERNEL_OPTION_HEADERS -include opt_global.h
 CFLAGS_PARAM_INLINE_UNIT_GROWTH?=100
 CFLAGS_PARAM_LARGE_FUNCTION_GROWTH?=1000
-CFLAGS.gcc+= -fms-extensions -finline-limit=${INLINE_LIMIT}
+CFLAGS.gcc+= -finline-limit=${INLINE_LIMIT}
 CFLAGS.gcc+= --param inline-unit-growth=${CFLAGS_PARAM_INLINE_UNIT_GROWTH}
 CFLAGS.gcc+= --param large-function-growth=${CFLAGS_PARAM_LARGE_FUNCTION_GROWTH}
-CFLAGS.gcc+= -fms-extensions
 .if defined(CFLAGS_ARCH_PARAMS)
 CFLAGS.gcc+=${CFLAGS_ARCH_PARAMS}
 .endif

sys/conf/kmod.mk

@@ -139,7 +139,6 @@ CFLAGS+=	-include ${.OBJDIR}/opt_global.h
 CFLAGS+=	-I. -I${SYSDIR} -I${SYSDIR}/contrib/ck/include
 
 CFLAGS.gcc+=	-finline-limit=${INLINE_LIMIT}
-CFLAGS.gcc+=	-fms-extensions
 CFLAGS.gcc+= --param inline-unit-growth=100
 CFLAGS.gcc+= --param large-function-growth=1000
 

sys/modules/iser/Makefile

@@ -17,7 +17,6 @@ CFLAGS+= -I${SYSDIR}/ofed/include/uapi
 CFLAGS+= ${LINUXKPI_INCLUDES}
 CFLAGS+= -DCONFIG_INFINIBAND_USER_MEM
 CFLAGS+= -DINET6 -DINET
-CFLAGS+= -fms-extensions
 
 CFLAGS+=-DICL_KERNEL_PROXY
 

sys/modules/pms/Makefile

@@ -17,7 +17,6 @@
 	${SRCTOP}/sys/dev/pms/freebsd/driver/common
 
 CFLAGS+=-fno-builtin
-CFLAGS+=-fms-extensions
 
 CFLAGS+=-Wredundant-decls
 CFLAGS+=-Wunused-variable

sys/powerpc/conf/dpaa/config.dpaa

@@ -2,7 +2,7 @@
 files		"dpaa/files.dpaa"
 
 makeoptions DPAA_COMPILE_CMD="${LINUXKPI_C} ${DPAAWARNFLAGS} \
-	-Wno-cast-qual -Wno-unused-function -Wno-init-self -fms-extensions \
+	-Wno-cast-qual -Wno-unused-function -Wno-init-self \
 	-include $S/contrib/ncsw/build/dflags.h \
 	-Wno-error=missing-prototypes \
 	-I$S/contrib/ncsw/build/ \