Fix NetBSD build: Include missing header for va_list in 8cc.h
Fix NetBSD build: Include missing header for va_list in 8cc.h

This addresses:

cc -Wall -Wno-strict-aliasing -std=gnu11 -g -I. -O0 -DBUILD_DIR='"/public/8cc"'   -c -o main.o main.c
In file included from main.c:9:0:
8cc.h:311:26: error: unknown type name ‘va_list’
 char *vformat(char *fmt, va_list ap);
                          ^
<builtin>: recipe for target 'main.o' failed
gmake: *** [main.o] Error 1

rui314/8cc,rui314/8cc,rui314/8cc,rui314/8cc