qemu-arm: Support building in debug mode with DEBUG=1.

Fixes issue #6095.

ports/qemu-arm/Makefile

@@ -43,9 +43,9 @@ INC += -I$(BUILD)
 CFLAGS += $(INC) -Wall -Wpointer-arith -Wdouble-promotion -Wfloat-conversion -Werror -std=gnu99 $(COPT) \
 	 -ffunction-sections -fdata-sections
 
-#Debugging/Optimization
+# Debugging/Optimization
 ifeq ($(DEBUG), 1)
-CFLAGS += -g -DPENDSV_DEBUG
+CFLAGS += -g
 COPT = -O0
 else
 COPT += -Os -DNDEBUG

ports/qemu-arm/startup.c

@@ -1,4 +1,5 @@
 #include <stdint.h>
+#include <stdio.h>
 #include <stdlib.h>
 
 #include "uart.h"
@@ -73,6 +74,14 @@ __attribute__((naked)) void exit(int status) {
     }
 }
 
+#ifndef NDEBUG
+void __assert_func(const char *file, int line, const char *func, const char *expr) {
+    (void)func;
+    printf("Assertion '%s' failed, at file %s:%d\n", expr, file, line);
+    exit(1);
+}
+#endif
+
 // The following are needed for tinytest
 
 #include <stdio.h>