Connect libc/tests/time to the build and modify strptime test program a bit:
- add check for 0 in %d conversion
- add check for 0 in %l conversion
- address the fact that we (correctly) fail 61 in %S conversion
- disable timezone test cases as timezone conversions are non-standard and differ between implementations
This still fails for century/year conversions indicating issues with our strptime that need to be taken care of.