Use make's built-in `.DEFAULT_GOAL` variable to set default target(s)

Instead of using the phony `DEFAULT_GOAL` target, use make's special variable
`.DEFAULT_GOAL` to work around the problem of including arduino-cli.mk at the
top of the sketch makefile.

Signed-off-by: Michael Richters <gedankenexperimenter@gmail.com>

Makefile

@@ -36,7 +36,7 @@ ifneq ($(TEST_PATH),)
 TEST_PATH_ARG="TEST_PATH='$(TEST_PATH)'"
 endif
 
-DEFAULT_GOAL: smoke-sketches
+.DEFAULT_GOAL := smoke-sketches
 
 .PHONY: setup
 setup: $(ARDUINO_CLI_PATH) $(ARDUINO_DIRECTORIES_DATA)/arduino-cli.yaml install-arduino-core-avr install-arduino-core-kaleidoscope $(ARDUINO_DIRECTORIES_USER)/hardware/keyboardio/avr/boards.txt $(ARDUINO_DIRECTORIES_USER)/hardware/keyboardio/virtual/boards.txt 

etc/makefiles/arduino-cli.mk

@@ -114,9 +114,10 @@ endif
 .PHONY: configure-arduino-cli install-arduino-core-kaleidoscope install-arduino-core-avr
 .PHONY: stupid-workaround-for-make-inclusion-semantics
 
-stupid-workaround-for-make-inclusion-semantics: DEFAULT_GOAL
+stupid-workaround-for-make-inclusion-semantics:
 	@: # This is here so that the sketch makefile including this file doesn't
 	@: # default to arduino-cli installation as its priamry target
+	@echo "No default target specified; aborting. Please set the .DEFAULT_GOAL variable in your makefile."
 
 $(KALEIDOSCOPE_BIN_DIR)/arduino-cli:
 	$(QUIET) curl -fsSL https://raw.githubusercontent.com/arduino/arduino-cli/master/install.sh | BINDIR="$(KALEIDOSCOPE_BIN_DIR)" sh

etc/makefiles/sketch.mk

@@ -99,7 +99,7 @@ endif
 
 
 
-DEFAULT_GOAL: compile
+.DEFAULT_GOAL := compile
 
 
 #$(SKETCH_FILE_PATH):

tests/Makefile

@@ -39,6 +39,8 @@ MAKEFLAGS += --no-print-directory
 
 include $(top_dir)/etc/makefiles/arduino-cli.mk
 
+.DEFAULT_GOAL := all
+
 # If we start off in tests to run make all, the sketch makefiles guess the wrong location for
 # Kaliedoscope's makefiles
 KALEIDOSCOPE_ETC_DIR ?= $(top_dir)/etc