postgresql-libpq fails to build

[quyse]

Describe the bug

postgresql-libpq fails to build since #2354.

Steps To Reproduce

nix build --impure --expr '(import ./default.nix {}).pkgs.haskell-nix.snapshots."lts-22.44".postgresql-libpq.components.library'

results in:

error: builder for '/nix/store/ls27zh7cfy7ypd1qk3j6pay27qf4d6kp-postgresql-libpq-lib-postgresql-libpq-0.10.0.0.drv' failed with exit code 1;
       last 13 log lines:
       > Running phase: unpackPhase
       > unpacking source archive /nix/store/lz73xpjfvqlgnqjsn1d6pmmy2ipz9j9y-postgresql-libpq-0.10.0.0.tar.gz
       > source root is postgresql-libpq-0.10.0.0
       > setting SOURCE_DATE_EPOCH to timestamp 1000000000 of file "postgresql-libpq-0.10.0.0/test/Smoke.hs"
       > Running phase: patchPhase
       > '/build/.attr-0h9ydb7s8pfhl5kfs3rmmwnmpi49yyiw7jgr5dpw9rmvv8sy0f2b' -> 'postgresql-libpq.cabal'
       > Running phase: updateAutotoolsGnuConfigScriptsPhase
       > Running phase: configurePhase
       > Configure flags:
       > --prefix=/nix/store/5vlrskjh1hjqh1rkvlf0jfcx6vyv1v70-postgresql-libpq-lib-postgresql-libpq-0.10.0.0 lib:postgresql-libpq --extra-include-dirs=/nix/store/iw29rzj5fvhryzl30xzscc1h3khg8zln-postgresql-17.4-dev/include --extra-lib-dirs=/nix/store/imszrbiaybv826wqh57jg9s7mng8grmp-postgresql-17.4-lib/lib --package-db=clear --package-db=/build/tmp.KThHXfIcS2/lib/ghc-9.6.7/lib/package.conf.d --flags=-use-pkg-config --with-ghc=ghc --with-ghc-pkg=ghc-pkg --with-hsc2hs=hsc2hs --with-gcc=cc --with-ar=ar --with-strip=strip --disable-executable-stripping --disable-library-stripping --disable-library-profiling --disable-profiling --enable-static --enable-shared --disable-executable-dynamic --disable-coverage --enable-library-for-ghci --datadir=/nix/store/kw6hbi5hs8dbcmh5179lx186h4941vv0-postgresql-libpq-lib-postgresql-libpq-0.10.0.0-data/share/ghc-9.6.7 --enable-split-sections
       > Configuring library for postgresql-libpq-0.10.0.0..
       > Error: Setup: The program 'pg_config' is required but it could not be found.
       >
       For full logs, run:
         nix log /nix/store/ls27zh7cfy7ypd1qk3j6pay27qf4d6kp-postgresql-libpq-lib-postgresql-libpq-0.10.0.0.drv

Expected behavior

postgresql-libpq builds.

Additional context

Bisecting pointed to 008e8cc, which belongs to #2354. Bisecting the PR's branch points to 0d0c47c.