package/berkeleydb: fix build with gcc-15.x

Inspired by
https://src.fedoraproject.org/rpms/libdb/c/c250c61cc3d56c5cff7ba59308f46245a32bdc69

"GCC 15 defaults to C23.  The last release of this package was over a
 decade ago, and it is no longer maintained, therefore it should not be
 expected to compile to the latest standards."

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Julien Olivain <ju.o@free.fr>
(cherry picked from commit c1d422edde19d07d6406705b1a4b059125dba689)
Signed-off-by: Thomas Perale <thomas.perale@mind.be>

package/berkeleydb/berkeleydb.mk

@@ -26,6 +26,7 @@ BERKELEYDB_BINARIES = db_archive db_checkpoint db_deadlock db_dump \
 define BERKELEYDB_CONFIGURE_CMDS
 	(cd $(@D)/build_unix; rm -rf config.cache; \
 		$(TARGET_CONFIGURE_OPTS) \
+		CFLAGS="$(TARGET_CFLAGS) -std=gnu99" \
 		$(TARGET_CONFIGURE_ARGS) \
 		../dist/configure $(QUIET) \
 		--target=$(GNU_TARGET_NAME) \