this behavior (opening fds 0-2 for a suid program) is explicitly
allowed (but not required) by POSIX to protect badly-written suid
programs from clobbering files they later open.
this commit does add some cost in startup code, but the availability
of auxv and the security flag will be useful elsewhere in the future.
in particular auxv is needed for static-linked vdso support, which is
still waiting to be committed (sorry nik!)
thanks to mikachu
per POSIX:
The setenv() function shall fail if:
[EINVAL] The name argument is a null pointer, points to an empty
string, or points to a string containing an '=' character.
