libc: fix the test

Currently after cleaning the variables the environment will be always
set to the intEnviron as documented in __rebuild_environ.

Reported by:	lwhsu@, jenkins

lib/libc/tests/stdlib/clearenv_test.c

@@ -136,7 +136,7 @@ ATF_TC_BODY(clearenv__environ_null, tc)
 {
 
 	ATF_CHECK(clearenv() == 0);
-	ATF_CHECK(environ == NULL);
+	ATF_CHECK(environ != NULL);
 }
 
 ATF_TC_WITHOUT_HEAD(clearenv__putenv_vars);