[SV 62173] Fix archive tests for non-GNU systems

[SV 62173] Fix archive tests for non-GNU systems

Original patch from Dmitry Goncharov <dgoncharov@users.sf.net>

Fix the ar flags to match the default values in make.  If the
U option is supported, add it to the end not the beginning,
since ARFLAGS now starts with a "-".

* tests/test_driver.pl: Add defaults for global variables.
(get_osname): Preserve $osname if it's set from $^O
* tests/scripts/features/archive: Set the default arflags.
If "U" is available add it to the end of the flags.