Add apps-or-nuttx-Make.defs

This is a wrapper for apps/Make.defs or nuttx/Make.defs

Since apps/Make.defs include nuttx/Make.defs, we check if it the
apps dir is available and include it, otherwise we just include
nuttx/Make.defs and keep the old behavior.

This allows EXTRA_LIBS and some other system-wide tweaks be
applied in any apps and make it work with the nuttx Makefiles.

tools/apps-or-nuttx-Make.defs

@@ -0,0 +1,36 @@
+############################################################################
+# apps-or-nuttx-Make.defs
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.  The
+# ASF licenses this file to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance with the
+# License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+# License for the specific language governing permissions and limitations
+# under the License.
+#
+############################################################################
+
+-include $(TOPDIR)/.config
+# CONFIG_APPS_DIR can be over-ridden from the command line or in the .config file.
+# The default value of CONFIG_APPS_DIR is ../apps.  Ultimately, the application
+# will be built if APPDIR is defined.  APPDIR will be defined if a directory containing
+# a Makefile is found at the path provided by CONFIG_APPS_DIR
+
+ifeq ($(CONFIG_APPS_DIR),)
+CONFIG_APPS_DIR = $(TOPDIR)/../apps
+endif
+APPDIR := $(realpath ${shell if [ -r $(CONFIG_APPS_DIR)/Makefile ]; then echo "$(CONFIG_APPS_DIR)"; fi})
+
+ifeq ($(APPDIR),)
+include $(TOPDIR)/Make.defs
+else
+include $(APPDIR)/Make.defs
+endif