something wrong when "make buildworld"

i've just installed freebsd 5.2RELEASE ,cvsup "src-all" to 5.2-CURRENT.i also add
CFLAGS= -march=athlon-xp -O3 -pipe -fomit-frame-pointer 
CXXFLAGS+= -march=athlon-xp -O3 -pipe -fomit-frame-pointer 
into /etc/make.conf (i'm using amd2500+ cpu)
and then:
#cd /usr/src
#make buildworld
something wrong happend after a few minutes. 
--------------------------------------------------------------
>>> stage 4.2: building libraries
--------------------------------------------------------------
.....
===> lib/libc
...
cc -march=athlon-xp -O3 -pipe -fomit-frame-pointer  -I/usr/src/lib/libc/include
-I/usr/src/lib/libc/../../include -I/usr/src/lib/libc/i386 -D__DBINTERFACE_PRIVATE
-I/usr/src/lib/libc/../../contrib/gdtoa -DINET6 -I/usr/obj/usr/src/lib/libc
-DPOSIX_MISTAKE -I/usr/src/lib/libc/locale -DBROKEN_DES -DPORTMAP -DDES_BUILTIN
-I/usr/src/lib/libc/rpc -DYP -DHESIOD -Wsystem-headers -Werror -Wall
-Wno-format-y2k -Wno-uninitialized -c /usr/src/lib/libc/gen/getnetgrent.c
In file included from /usr/src/lib/libc/gen/getnetgrent.c:323:
/usr/src/lib/libc/gen/getnetgrent.c: In function `innetgr':
/usr/src/lib/libc/gen/getnetgrent.c:308: warning: passing arg of `_buildkey'
discards qualifiers from pointer target type
/usr/src/lib/libc/gen/getnetgrent.c:308: warning: passing arg of `_buildkey'
discards qualifiers from pointer target type
In file included from /usr/src/lib/libc/gen/getnetgrent.c:303:
/usr/src/lib/libc/gen/getnetgrent.c:284: warning: passing arg of `_listmatch'
discards qualifiers from pointer target type
*** Error code 1

Stop in /usr/src/lib/libc.
*** Error code 1

Stop in /usr/src/lib.
*** Error code 1

Stop in /usr/src.
*** Error code 1

Stop in /usr/src.
*** Error code 1

Stop in /usr/src.
*** Error code 1

Stop in /usr/src.
any one can help me?thanks very much :)