Unable to build libpg_query-sys against system libpg_query in v1.1.1

[lubo]

Hi. I'm maintainer of https://aur.archlinux.org/packages/squawk-cli. In chdsbd/libpg_query-sys@e29418b, LIBPG_QUERY_PATH environmental variable has been removed and libpg_query is always built from source. This is undesirable, as I don't wanna deal with all the issues that stem from bundling of native dependencies. Would it be possible to get back the option to build libpg_query-sys against system libpg_query?

[chdsbd]

@lubo Thanks for the report!

Is it possible for you to test with this PR? #358