Update tests to use the new format of printing a TimeValue. It's a bit
odd to have the output of 'llvm-ar tv' depend on the format of
TimeValue::str(), but that's what we have today. If anyone needs the
output to remain compatible with GNU ar or old versions of llvm-ar, just
shout and I'll switch the code to manually format its times.

Note that there isn't a portable format -- Mac and GNU have different
formats at least (thanks Rafael!) so...
Update the Windows TimeValue formatting to match the new formatting on
Unix-like OSes.