The ninstall... function is not callable for some reason, so we need to copy
the definition when using install_cmd.

diff --git a/config/rules.mk b/config/rules.mk
--- a/config/rules.mk
+++ b/config/rules.mk
@@ -1350,7 +1350,7 @@
 nsinstall_is_usable = $(if $(wildcard $(DEPTH)/config/nsinstall$(HOST_BIN_SUFFIX)),yes)
 
 define install_cmd_override
-$(1): install_cmd = $$(if $$(nsinstall_is_usable),$$(INSTALL),$$(NSINSTALL_PY) -t) $$(1)
+$(1): install_cmd = $$(if $(wildcard $(DIST)/bin/nsinstall$(HOST_BIN_SUFFIX)),$$(INSTALL),$$(NSINSTALL_PY) -t) $$(1)
 endef
 endif
 endif