postgresql: update to 18.6

Security release from 18.4 (18.5 was never released, pulled post-wrap
due to a regression). A dump/restore is not required for those running
18.x, but see the migration notes below for the first three security
fixes, GIN index reltuples corruption, and btree_gist/ltree reindexing.

- restrict logical decoding output plugins to a new
  output_plugin_libraries allowlist; previously a replication user
  could load any library for logical decoding (CVE-2026-6471)
- fix contrib/pgcrypto PGP encryption to detect unsupported ciphers;
  previously an OpenSSL cipher rejection (e.g. FIPS mode) was ignored
  and pgcrypto silently XORed plaintext instead of encrypting it
  (CVE-2026-14663)
- fix psql to skip in-line data following a scripted
  "COPY ... FROM STDIN" even when the COPY fails before
  PGRES_COPY_IN, closing a SQL-injection hazard in scripts that
  exercise failing COPY commands (CVE-2026-6464)
- cross-check the output row type of a portal running EXECUTE/FETCH;
  divergent declared row types between the outer and inner portal
  could lead to server memory disclosure and arbitrary code execution
  (CVE-2026-16239)
- fix a buffer overrun with a long time zone abbreviation in
  to_char(), which could crash the server or be exploited for
  arbitrary code execution (CVE-2026-14669)

Plus a variety of other fixes from 18.4; see the upstream release notes
for the complete list.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

libs/postgresql/Makefile

@@ -5,7 +5,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=postgresql
-PKG_VERSION:=18.4
+PKG_VERSION:=18.6
 PKG_RELEASE:=1
 
 PKG_MAINTAINER:=Daniel Golle <daniel@makrotopia.org>
@@ -16,7 +16,7 @@ PKG_CPE_ID:=cpe:/a:postgresql:postgresql
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2
 PKG_SOURCE_URL:=https://ftp.postgresql.org/pub/source/v$(PKG_VERSION)
 
-PKG_HASH:=81a81ec695fb0c7901407defaa1d2f7973617154cf27ba74e3a7ab8e64436094
+PKG_HASH:=555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f
 
 PKG_BUILD_FLAGS:=no-mips16
 PKG_FIXUP:=autoreconf