pgsql: pg_ctl: Silence warnings about unused global variables

pg_ctl: Silence warnings about unused global variables

Several global variables are only used in Windows build. This causes
-Wunused-but-set-global warnings that the new clang 23 enables via
-Wall.

This commit marks these with an unused attribute to silence the
warnings.

(In the master branch, this is addressed differently, but for
backpatching, this just silences the warnings without any behavior
change.)

Reviewed-by: Andreas Karlsson <andreas(at)proxel(dot)se>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://www.postgresql.org/message-id/flat/eb013f9d-2247-444e-8815-9d17b4ce78e7%40eisentraut.org

Branch
------
REL_19_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/fbaeb88978f023e724bef1ce74fc46c65841401c

Modified Files
--------------
src/bin/pg_ctl/pg_ctl.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)