NetBSD 10.0_BETA w/gcc can't build NetBSD 10.0_BETA w/clang

I'm trying to build NetBSD 10.0_BETA with clang from NetBSD 10.0_BETA (Sat 
Jun 24 02:46:39 UTC 2023) with gcc, and it fails here:

--- pixman-fast-path.po ---
/usr/xsrc/external/mit/pixman/dist/pixman/pixman-fast-path.c:2614:32: 
error: shifting a negative signed value is undefined 
[-Werror,-Wshift-negative-value]
     while (buffer < end && x < pixman_fixed_minus_1)
                                ^~~~~~~~~~~~~~~~~~~~
/usr/xsrc/external/mit/pixman/dist/pixman/pixman.h:128:32: note: expanded 
from macro 'pixman_fixed_minus_1'
#define pixman_fixed_minus_1            (pixman_int_to_fixed(-1))
                                          ^~~~~~~~~~~~~~~~~~~~~~~
/usr/xsrc/external/mit/pixman/dist/pixman/pixman.h:130:56: note: expanded 
from macro 'pixman_int_to_fixed'
#define pixman_int_to_fixed(i)          ((pixman_fixed_t) ((i) << 16))
                                                            ~~~ ^
1 error generated.

*** Failed target: pixman-fast-path.po
*** Failed commands:
 	${_MKTARGET_COMPILE}
 	=> @echo '#  ' "compile " pixman/pixman-fast-path.po
 	${COMPILE.c} ${PROFFLAGS} ${COPTS.${.IMPSRC:T}} 
${CPUFLAGS.${.IMPSRC:T}} ${CPPFLAGS.${.IMPSRC:T}} ${PGFLAGS} ${.IMPSRC} 
${OBJECT_TARGET}
 	=> /usr/src/../tools/bin/x86_64--netbsd-clang -O2  -std=gnu99 
-Werror   -fPIE -fno-strict-aliasing   --sysroot=/usr/src/../dest-amd64 
-DUSE_SSE2 -DUSE_SSSE3 -DHAVE_CONFIG_H 
-I/usr/xsrc/external/mit/pixman/dist/../include 
-I/usr/xsrc/external/mit/pixman/dist/../combine 
-I/usr/xsrc/external/mit/pixman/dist/pixman -DHAVE_PTHREAD_SETSPECIFIC 
-DCSRG_BASED -DFUNCPROTO=15 -DNARROWPROTO 
-I/usr/src/../dest-amd64/usr/X11R7/include -D__AMD64__ -c -DGPROF -DPROF 
-pg -fPIC /usr/xsrc/external/mit/pixman/dist/pixman/pixman-fast-path.c -o 
pixman-fast-path.po.o
 	${CTFCONVERT_RUN}
 	=> /usr/src/../tools/bin/nbctfconvert -g -L VERSION -o 
pixman-fast-path.po pixman-fast-path.po.o && rm -f pixman-fast-path.po.o
 	${OBJCOPY} ${OBJCOPYLIBFLAGS} ${.TARGET}
 	=> /usr/src/../tools/bin/x86_64--netbsd-objcopy -X 
pixman-fast-path.po
*** [pixman-fast-path.po] Error code 1

nbmake[6]: stopped in /usr/src/external/mit/xorg/lib/pixman


Thanks,
John