pgsql: Fix type confusion in guc_var_compare()

Fix type confusion in guc_var_compare()

Before this change guc_var_compare() cast the input arguments to
const struct config_generic *. That's not quite right however, as the input
on one side is often just a char * on one side.

Instead just use char *, the first field in config_generic.

This fixes a -Warray-bounds warning with some versions of gcc. While the
warning is only known to be triggered for <= 15, the issue the warning points
out seems real, so apply the fix everywhere.

Author: Nazir Bilal Yavuz <byavuz81(at)gmail(dot)com>
Reported-by: Erik Rijkers <er(at)xs4all(dot)nl>
Suggested-by: Andres Freund <andres(at)anarazel(dot)de>
Discussion: https://postgr.es/m/a74a1a0d-0fd2-3649-5224-4f754e8f91aa%40xs4all.nl

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/b9f3db23b7b5c7f522162e16482b096d9c930f80

Modified Files
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src/backend/utils/misc/guc.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)