Makefile: Don't add _install_tmp to itself on make install.

When OpenWrt builder uses make install, some conditions cause make install to
include _install_tmp as a submodule and causes cp to error with
cp: _install_tmp/<file>.py is the same file as <full-path>/<file>.py

Author: ticpu

Makefile

@@ -11,6 +11,7 @@ install:
 	else \
 	    for d in $$(find -maxdepth 1 -type d ! -name ".*"); do \
 	        echo $$d; \
+	        [ "$$d" = "./_install_tmp" ] && continue; \
 	        (cd $$d; sh -c $(CMD)); \
 	    done \
 	fi