pgsql: Add missing dependencies to meson headerscheck target

Add missing dependencies to meson headerscheck target

These checks compile headers, so all the headers they might include
need to have been generated. The makefile target does that, but the
meson implementation didn't do that. (Arguably a bit of a bug in
commit e82fc27e095.) Add the required dependencies so that meson
compile headerscheck works in an unbuilt tree as well (as is
documented).

This backpatches master/20 commit 0f3b42ce806 to 19, which is where
e82fc27e095, the commit being fixed, landed.

Reviewed-by: Nazir Bilal Yavuz <byavuz81(at)gmail(dot)com>
Discussion: https://www.postgresql.org/message-id/flat/e52e2c29-4834-4c64-a200-eddcba38fb4d%40eisentraut.org
Backpatch-through: 19

Branch
------
REL_19_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/e90a17e11f5dd053032a1dbdf528108492de4d37
Author: Peter Eisentraut <peter(at)eisentraut(dot)org>

Modified Files
--------------
meson.build | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)