there's minor bitrot in the Mkvcbuild.pm change, making cfbot unhappy.
As for the patch, I don't have much comments. I'm wondering if it'd be useful to indicate which timing source was actually used for EXPLAIN ANALYZE, say something like:
Planning time: 0.197 ms Execution time: 0.225 ms Timing source: clock_gettime (or tsc)
There has been a proposal to expose this as a GUC (or perhaps as explain option), to allow users to pick what timing source to use. I wouldn't go that far - AFAICS is this is meant to be universally better when available. But knowing which source was used seems useful.
