samba4: ensure that copied cache.txt is writable

If the Buildroot tree is read-only, then cache.txt is copied read-only into
the build directory, and the configuration step fails.  Fix this in the
same way we do in other places, by opening permissions as we copy the file
using $(INSTALL).

Signed-off-by: Danomi Manchego <danomimanchego123@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/samba4/samba4.mk

@@ -86,7 +86,7 @@ endef
 SAMBA4_POST_INSTALL_TARGET_HOOKS += SAMBA4_REMOVE_CTDB_TESTS
 
 define SAMBA4_CONFIGURE_CMDS
-	cp package/samba4/samba4-cache.txt $(@D)/cache.txt;
+	$(INSTALL) -m 0644 package/samba4/samba4-cache.txt $(@D)/cache.txt;
 	echo 'Checking uname machine type: $(BR2_ARCH)' >>$(@D)/cache.txt;
 	(cd $(@D); \
 		PYTHON_CONFIG="$(STAGING_DIR)/usr/bin/python-config" \