gpt/zfs boot blocks: reduce optimizing CFLAGS to -O1

gpt and zfs boot blocks are not nearly as size-constrained as boot2
from which they inherited their current optimization and anti-optimization
options.  As such the current options do not provide any benefit, but
make debugging of the code much harder.
Also, it has been demonstrated that combination of -mrtd and
-fno-unit-at-a-time may result in mis-compilation of the boot code
with the current base gcc.

Additionally, intermediate assembly file filtering is removed for
zfsboot.

The new boot blocks are all compile- and boot- tested using qemu.
gptzfsboot is tested with real hardware.

Reported by:	Peter Jeremy <peterjeremy@acm.org> [miscompilation]
Discussed with:	bde, jhb
Tested by:	Sebastian Chmielewski <chmielsster@gmail.com> [gptzfsboot]
Approved by:	re (kib)
MFC after:	3 weeks

sys/boot/i386/gptboot/Makefile

@@ -20,12 +20,7 @@ GPTBOOT_UFS?=	UFS1_AND_UFS2
 #GPTBOOT_UFS?=	UFS1_ONLY
 
 CFLAGS=	-DBOOTPROG=\"gptboot\" \
-	-Os \
-	-fno-guess-branch-probability \
-	-fomit-frame-pointer \
-	-fno-unit-at-a-time \
-	-mno-align-long-strings \
-	-mrtd \
+	-O1 \
 	-DGPT \
 	-D${GPTBOOT_UFS} \
 	-DSIOPRT=${BOOT_COMCONSOLE_PORT} \

sys/boot/i386/gptzfsboot/Makefile

@@ -17,12 +17,7 @@ ORG1=	0x7c00
 ORG2=	0x0
 
 CFLAGS=	-DBOOTPROG=\"gptzfsboot\" \
-	-Os \
-	-fno-guess-branch-probability \
-	-fomit-frame-pointer \
-	-fno-unit-at-a-time \
-	-mno-align-long-strings \
-	-mrtd \
+	-O1 \
 	-DGPT -DBOOT2 \
 	-DSIOPRT=${BOOT_COMCONSOLE_PORT} \
 	-DSIOFMT=${B2SIOFMT} \

sys/boot/i386/zfsboot/Makefile

@@ -15,12 +15,7 @@ ORG1=	0x7c00
 ORG2=	0x2000
 
 CFLAGS=	-DBOOTPROG=\"zfsboot\" \
-	-Os \
-	-fno-guess-branch-probability \
-	-fomit-frame-pointer \
-	-fno-unit-at-a-time \
-	-mno-align-long-strings \
-	-mrtd \
+	-O1 \
 	-DBOOT2 \
 	-DSIOPRT=${BOOT_COMCONSOLE_PORT} \
 	-DSIOFMT=${B2SIOFMT} \
@@ -85,20 +80,10 @@ zfsboot.bin: zfsboot.out
 zfsboot.out: ${BTXCRT} zfsboot.o sio.o drv.o cons.o util.o
 	${LD} ${LDFLAGS} -Ttext ${ORG2} -o ${.TARGET} ${.ALLSRC} ${LIBSTAND}
 
-zfsboot.o: zfsboot.s
-.if ${CC:T:Mclang} == "clang"
-	${CC} ${ACFLAGS} -c zfsboot.s
-.endif
-
 SRCS=	zfsboot.c
 
-zfsboot.s: zfsboot.c ${.CURDIR}/../../zfs/zfsimpl.c
-	${CC} ${CFLAGS} -S -o zfsboot.s.tmp ${.CURDIR}/zfsboot.c
-	sed -e '/align/d' -e '/nop/d' < zfsboot.s.tmp > zfsboot.s
-	rm -f zfsboot.s.tmp
-
 .if ${MACHINE_CPUARCH} == "amd64"
-beforedepend zfsboot.s: machine
+beforedepend zfsboot.o: machine
 CLEANFILES+=	machine
 machine:
 	ln -sf ${.CURDIR}/../../../i386/include machine