uclibc: Fix getopt implementations conditional compilation

There's no way to disable getsubopt in uClibc 0.9.33.2: either GNU or
SUSv3 getsubopt is always built.

Properly exclude SUSv3 getsubopt implementation when GNU getopt is
selected.
Exclude GNU getsubopt when SUSv3 getopt is selected. Honor getopt_long
configuration.

This brings UCLIBC_HAS_GNU_GETOPT, UCLIBC_HAS_GNU_GETSUBOPT and
UCLIBC_HAS_GETOPT_LONG handling in sync with uClibc and uClibc-ng tips.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>