Cross-build on macOS fails

[Adam <adam%netbsd.org@localhost>]

In file included from /dist/src/lib/libc/time/zic.c:9:
In file included from /dist/tools.aarch64/include/compat/nbtool_config.h:987:
/dist/src/tools/compat/compat_defs.h:620:7: warning: incompatible redeclaration of library function 'mempcpy' [-Wincompatible-library-redeclaration]
  620 | char *mempcpy(void *, const void *, size_t);
      |       ^
/dist/src/tools/compat/compat_defs.h:620:7: note: 'mempcpy' is a builtin with type 'void *(void *, const void *, unsigned long)'
In file included from /dist/src/lib/libc/time/zic.c:35:
/dist/src/lib/libc/time/private.h:858:1: error: static declaration of 'mempcpy' follows non-static declaration
  858 | mempcpy(void *restrict s1, void const *restrict s2, size_t n)
      | ^
/dist/src/tools/compat/compat_defs.h:620:7: note: previous declaration is here
  620 | char *mempcpy(void *, const void *, size_t);
      |       ^
1 warning and 1 error generated.
--- zic.lo ---

*** Failed target: zic.lo
*** In directory: /dist/src/tools/zic
*** Failed commands:
${_MKTARGET_COMPILE}
=> @# "compile " zic/zic.lo
${HOST_COMPILE.c} -o ${.TARGET}.o ${COPTS.${.IMPSRC:T}} ${CPUFLAGS.${.IMPSRC:T}} ${CPPFLAGS.${.IMPSRC:T}} ${.IMPSRC}
=> /usr/bin/clang -O2 -fno-stack-protector -no-cpp-precomp  -DHAVE_GETTEXT=0 -I/dist/tools.aarch64/include/compat -I/dist/src/tools/compat -DHAVE_NBTOOL_CONFIG_H=1 -D_FILE_OFFSET_BITS=64 -DREPORT_BUGS_TO=\"gnats%netbsd.org@localhost\" -DPKGVERSION='"(tzcode) "' -DTZVERSION='"2025c"' -DZIC_BLOAT_DEFAULT='"slim"' -D_KERNTYPES -c -o zic.lo.o -Wno-format-nonliteral   /dist/src/lib/libc/time/zic.c
${MV} ${.TARGET}.o ${.TARGET}
=> mv -f zic.lo.o zic.lo
*** [zic.lo] Error code 1