syscalls: fix testcases which take TCONF as TFAIL

This issue was introduced by commit:
6f6878f4e1406d79cae53564777c5e1245d2a124 In this commit, we took TCONF
as a special state, to let user know the real LTP test coverage.

But setreuid04.c, setreuid05.c, setreuid07.c and setfsuid04.c do real
test work in child process, if 16-bit version of setreuid or setfsuid is
not supported on some platforms, child process will return a TCONF(see
syscalls/utils/compat_16.h), then parent process will get a non-zero
return value and take it as TFAIL directly, fix this.

Signed-off-by: Xiaoguang Wang <wangxg.fnst@cn.fujitsu.com>