Pipeline support breaks build

[hennevogel]

#403 breaks the build for me complaining about PGRES_PIPELINE_SYNC etc. being undeclared (and judging from a quick look at the PR it is).

https://gist.github.com/hennevogel/d22b0e16a87b32914075754f700e0934

[larskanis]

The output tells that the version of libpq installed on your system is from PostgreSQL-14 while the header files are from an version 13. This doesn't work. Check if there is another libpq.so file in some system directory!

[hennevogel]

After sorting this out (everything is on PG12 now) it's still happening. I've updated the gist.

[hennevogel]

@larskanis 💐