* testsuite/ld-scripts/crossref.exp: Initialize flags to
[big_or_little_endian].
* testsuite/ld-undefined/undefined.exp: Ditto, and include $flags
in ld invocations.
* testsuite/lib/ld-lib.exp (big_or_little_endian): Recognize -EB,
-eb, EL and el.
(is_endian_output_format): New function.
(default_ld_link): Set flags to [big_or_little_endian] only if ld
is being invoked such that the output format being used is of
known endianness.
(default_ld_simple_link): Ditto.
