elf: Fix glibc-hwcaps priorities with cache flags mismatches [BZ #27046]

If lib->flags (in the cache) did not match GLRO (dl_correct_cache_id),
searching for further glibc-hwcaps entries did not happen, and it
was possible that the best glibc-hwcaps was not found.  By accident,
this causes a test failure for elf/tst-glibc-hwcaps-prepend-cache
on armv7l.

This commit changes the cache lookup logic to continue searching
if (a) no match has been found, (b) a named glibc-hwcaps match
has been found(), or (c) non-glibc-hwcaps match has been found
and the entry flags and cache default flags do not match.

_DL_CACHE_DEFAULT_ID is used instead of GLRO (dl_correct_cache_id)
because the latter is only written once on i386 if loading
of libc.so.5 libraries is selected, so GLRO (dl_correct_cache_id)
should probably removed in a future change.

Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>