dev-db/postgresql: build w/ -std=gnu17

Upcoming GCC 15 defaults to -std=gnu23 which pg fails to build with. Go
back to the default -std=gnu17 (i.e. a noop for older GCCs) until the
upstream report I've sent is fixed.

Sent that to pgsql-bugs but it's still in the moderation queue for now,
I'll update with the link once it's through.

Signed-off-by: Sam James <sam@gentoo.org>

dev-db/postgresql/postgresql-17.1.ebuild

@@ -128,6 +128,11 @@ src_prepare() {
 }
 
 src_configure() {
+	# Fails to build with C23, fallback to the old default in < GCC 15
+	# for now. Reported upstream to pgsql-bugs ML but not yet through
+	# moderation filter.
+	append-cflags -std=gnu17
+
 	case ${CHOST} in
 		*-darwin*|*-solaris*)
 			use nls && append-libs intl

dev-db/postgresql/postgresql-9999.ebuild

@@ -143,6 +143,11 @@ src_prepare() {
 }
 
 src_configure() {
+	# Fails to build with C23, fallback to the old default in < GCC 15
+	# for now. Reported upstream to pgsql-bugs ML but not yet through
+	# moderation filter.
+	append-cflags -std=gnu17
+
 	case ${CHOST} in
 		*-darwin*|*-solaris*)
 			use nls && append-libs intl