Fix setenv/getenv/unsetenv to be OpenGroup compliant:
* libc/include/stdlib.h (unsetenv, _unsetenv_r): Redefine with integer
return types.
* libc/stdlib/getenv_r.c (_findenv_r): Do no special processing with
names that contain equal chars.
* libc/stdlib/setenv.c: Redefine _unsetenv_r as returning int.
* libc/stdlib/setenv_r.c (_setenv_r): Return -1 and set errno to
EINVAL if name contains an equal sign. Do not remove any equal signs
from the value.
(_unsetenv_r): Modified to return int. Return -1 and set EINVAL
if name contains equal sign. Return -1 if no variable(s) were found
and return 0 otherwise.