env(1): unbreak build of 2_2 release branch under HEAD

env(1): unbreak build of 2_2 release branch under HEAD

The problem exhibits when running an old env(1), which is part of
the bootstrap tools of 2_2, in a host system with new libc/setenv(3).

When a "value=name" string is supplied to the old env(1), it doesn't
actually break it into 2 pieces (ie null terminate on '='). It just
creates two pointers, one pointing to the start of "value" and one
to the start of "name". These pointers are subsequently passed to
setenv(3). When new setenv(3) encounters the '=' character as part
of the "name", it fails with EINVAL. Which is exactly what it should
do, complying with the POSIX standard.

This patch has been tested and found to:
1) unbreak the build of 2_2 release branch under HEAD
2) not affect (i.e., break) the build of 2_2 under a 2.2 host system
3) not affect (i.e., break) the build of 2_2 under a 2.0 host system