If you're using gmake 4.0 or newer, display simulator test output nicer

Makefile

@@ -18,6 +18,11 @@ MAKEFLAGS += --no-builtin-rules
 
 .SUFFIXES:
 
+# GNU Make earlier than 4.0 don't have the output-sync option, but we need it
+# to make parallel simulator test output readable. (otherwise it gets interleaved)
+ifeq ($(shell test $(firstword $(subst ., ,$(MAKE_VERSION))) -ge 4; echo $$?),0)
+SUBDIR_MAKEFLAGS+=--output-sync=target
+endif
 
 include $(dir $(abspath $(lastword $(MAKEFILE_LIST))))/etc/makefiles/arduino-cli.mk
 

tests/Makefile

@@ -94,6 +94,3 @@ Makefile:
 
 ${TESTS}: ${libcommon_a} googletest
 	$(QUIET) ${MAKE} -f ${top_dir}/testing/makefiles/testcase.mk -C $@ testcase=$@ build run
-
-%+run:
-	$(QUIET) ${MAKE} -s -f ${top_dir}/testing/makefiles/testcase.mk -C $* testcase=$* run