> 3.2.3.1 explicitly talks about enabling it. I can't help you with the
> Visual Studio problem though, but I doubt that without additional work
> e.g. a compiler wrapper it can work.

c89 is a compiler wrapper.
more `which c89';
....
#
# c89 -- Interface to map c89 options (plus a few "UNIX" options) to
#        MSVC 4.0.
#

problem is
bmake.boot was compiled by gcc
    gcc -D_ALL_SOURCE *.o lst.lib/*.o -o bmake.boot  -L../../libnbcompat -lnbcompat
then pass CC=gcc to bmake.boot 
    CC="gcc -D_ALL_SOURCE" LIBC= MAKEFLAGS= MAKESYSPATH=`pwd`/mk:mk:/usr/pkg/share/mk:/usr/share/mk:/usr/local/share/mk:/opt/share/mk ./bmake.boot -f Makefile
    c89 -O -D_PATH_DEFSYSPATH=\"/usr/pkg/share/mk\" -I. -I/var/tmp/obj/pkgsrc/bmake -DHAVE_CONFIG_H  -I../../libnbcompat -I/var/tmp/obj/pkgsrc/bmake/missing -DNEED_HOST_CDEFS_H  -DMAKE_NATIVE  -DSIGNAL_FLAGS=SA_RESTART  -Werror  -c /var/tmp/obj/pkgsrc/bmake/arch.c

Why c89 was called?
Find & grep and no "c89" was found.
And
    % bmake.boot -V CC
    gcc

....Ah,

CC should be defined as make var rather than env var?
by hand,
    LIBC= MAKEFLAGS= MAKESYSPATH=`pwd`/mk:mk:/usr/pkg/share/mk:/usr/share/mk:/usr/local/share/mk:/opt/share/mk ./bmake.boot -f Makefile CC="gcc -D_ALL_SOURCE" 
compile OK by using gcc.

Hmmm...?
--
OBATA Akio
obata@lins.jp