Update to rra-c-util 5.6 and C TAP Harness 3.2

Update to rra-c-util 5.6:

* Suppress warnings from Kerberos headers in non-system paths.
* Fix probing for Heimdal's libroken to work with older versions.
* Fix Kerberos header detection if root or include paths are given.
* Pass --deps to krb5-config in the non-reduced-dependencies case.
* Provide a reallocarray replacement for platforms without it.
* Use reallocarray where appropriate.
* Drop checks for NULL before freeing pointers.
* Drop explicit pointer initialization to NULL and rely on calloc.
* Check the return status of snprintf and vsnprintf properly.
* Preserve errno if snprintf fails in vasprintf replacement.
* Suppress a dummy symbol in the client library that could leak.
* Fix syntax errors when building with a C++ compiler.
* Avoid test suite failures where tested functions are macros.

Update to C TAP Harness 3.2:

* Reopen standard input to /dev/null when running a test list.
* Don't leak extraneous file descriptors to tests.
* Suppress lazy plans and test summaries if the test failed with bail.
* bail and sysbail now exit with status 255 to match Test::More.
* 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.