Allow customizing QEMU echr option

Author: gsingh93

Diff for: Makefile

@@ -302,6 +302,7 @@ GDB ?= 0
 INITRD ?=
 RDINIT ?= /sbin/init
 QEMU_KERNEL_IMAGE ?= $(KERNEL_IMAGE)
+ECHR ?= 1
 
 QEMU_ARGS := \
   -m $(MEM) \
@@ -311,6 +312,7 @@ QEMU_ARGS := \
   -kernel $(QEMU_KERNEL_IMAGE) \
   -netdev user,id=eth0,hostfwd=tcp::7777-:7777,hostfwd=tcp::2222-:22,hostfwd=tcp::2223-:23 -device virtio-net-pci,netdev=eth0 \
   -virtfs local,security_model=mapped-xattr,path=$(SHARED_DIR),mount_tag=shared \
+  -echr $(ECHR) \
   $(QEMU_EXTRA_ARGS)
 
 ifneq ($(INITRD),)