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_16_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/8e4d7e7baa46fde0cc140e475a3b2647e72580af

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