make: delete emptyarchive after test

Makefile.include

@@ -131,7 +131,8 @@ CFLAGS += -DCPU_$(CPUDEF)=\"$(CPU)\" -DRIOT_CPU=CPU_$(CPUDEF)
 CFLAGS += -DMCU_$(MCUDEF)=\"$(MCU)\" -DRIOT_MCU=MCU_$(MCUDEF)
 
 # OSX fails to create empty archives. Provide a wrapper to catch that error.
-ifneq (0, $(shell mkdir -p $(BINDIR); $(AR) rc $(BINDIR)empty-archive.a 2> /dev/null; echo $$?))
+ifneq (0, $(shell mkdir -p $(BINDIR); $(AR) rc $(BINDIR)empty-archive.a 2> /dev/null; \
+            echo $$?; rm -f $(BINDIR)empty-archive.a 2>&1 > /dev/null))
 	AR := $(RIOTBASE)/dist/ar-wrapper $(AR)
 endif