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_18_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/810e63b1443c928fa7889054c46d0f3df10b32ef

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