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_15_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/8032e8e89456319bc0384c322ebf53ffd666d329

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