Fix gcc build
https://ci.freebsd.org/job/FreeBSD-head-amd64-gcc/10338/console :
In file included from /workspace/src/stand/efi/boot1/boot1.c:34:0:
/workspace/src/stand/efi/boot1/boot_module.h:112:12: error: redundant redeclaration of 'vsnprintf' [-Werror=redundant-decls]
extern int vsnprintf(char *str, size_t sz, const char *fmt, va_list ap);
^~~~~~~~~
In file included from /workspace/src/stand/efi/boot1/boot1.c:28:0:
/workspace/src/stand/libsa/stand.h:276:12: note: previous declaration of 'vsnprintf' was here
extern int vsnprintf(char *buf, size_t size, const char *cfmt, __va_list);
^~~~~~~~~I see most files already include stand.h so I suspect we can remove redeclaration in boot_module.h (or have a #ifndef guard?)