Update to rra-c-util 4.12:
* Better error messages from xasprintf on failure to format output.
* Check return status of vsnprintf properly.
* Significant improvements to POD tests.
* Avoid leaking a dummy symbol from the portability layer.
* Probe for Kerberos headers with file existence checks.
Update to C TAP Harness 2.3:
* runtests now treats the command line as a list of tests by default.
* The full test executable path can now be passed to runtests -o.
* Improved harness output for tests with lazy plans.
* Improved harness output to a terminal for some abort cases.
* Flush harness output after each test even when not on a terminal.
* bail and sysbail now exit with status 255 to match Test::More.
* Suppress lazy plans and test summaries if the test failed with bail.
* Add warn_unused_result gcc attributes to relevant functions.