selftests/nolibc: add EXPECT_PTREQ, EXPECT_PTRNE and EXPECT_PTRER

The syscalls like sbrk() and mmap() return pointers, to test them, more
pointer compare test macros are required, add them:

- EXPECT_PTREQ() expects two equal pointers.
- EXPECT_PTRNE() expects two non-equal pointers.
- EXPECT_PTRER() expects failure with a specified errno.
- EXPECT_PTRER2() expects failure with one of two specified errnos.

Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>