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

Commit [1] fixed berkeleydb target build with gcc-15.x.
The host variant package also fails when building with host gcc-15.x.

This commit fixes the issue by replicating the same fix for the package
host variant.

Fixes:
https://autobuild.buildroot.org/results/a8051600ab95a63c852960f8dace757b16c665f0/

[1] https://gitlab.com/buildroot.org/buildroot/-/commit/c1d422edde19d07d6406705b1a4b059125dba689

Reviewed-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>

package/berkeleydb/berkeleydb.mk

@@ -51,6 +51,7 @@ endef
 define HOST_BERKELEYDB_CONFIGURE_CMDS
 	(cd $(@D)/build_unix; rm -rf config.cache; \
 		$(HOST_CONFIGURE_OPTS) \
+		CFLAGS="$(HOST_CFLAGS) -std=gnu99" \
 		../dist/configure $(QUIET) \
 		--prefix=$(HOST_DIR) \
 		--with-gnu-ld \