使得DragonOS kernel 能为riscv64编译通过(尚未能启动) (#457)

* 使得DragonOS kernel 能为riscv64编译通过(尚未能启动)

* 修正了系统调用号声明不正确的问题，同时添加了编译配置文档

env.mk

@@ -0,0 +1,48 @@
+
+ifeq ($(ARCH), )
+# ！！！！在这里设置ARCH，可选x86_64和riscv64
+# !!!!!!!如果不同时调整这里以及vscode的settings.json，那么自动补全和检查将会失效
+export ARCH=x86_64
+endif
+
+ifeq ($(EMULATOR), )
+export EMULATOR=__NO_EMULATION__
+endif
+
+# 设置编译器
+ifeq ($(ARCH), x86_64)
+
+export CC=$(DragonOS_GCC)/x86_64-elf-gcc
+export LD=ld
+export AS=$(DragonOS_GCC)/x86_64-elf-as
+export NM=$(DragonOS_GCC)/x86_64-elf-nm
+export AR=$(DragonOS_GCC)/x86_64-elf-ar
+export OBJCOPY=$(DragonOS_GCC)/x86_64-elf-objcopy
+
+else ifeq ($(ARCH), riscv64)
+
+export CC=riscv64-unknown-elf-gcc
+export LD=riscv64-unknown-elf-ld
+export AS=riscv64-unknown-elf-as
+export NM=riscv64-unknown-elf-nm
+export AR=riscv64-unknown-elf-ar
+export OBJCOPY=riscv64-unknown-elf-objcopy
+
+endif
+
+
+export DEBUG=DEBUG
+
+export CFLAGS_DEFINE_ARCH="__$(ARCH)__"
+
+export GLOBAL_CFLAGS := -fno-builtin -fno-stack-protector -D $(CFLAGS_DEFINE_ARCH) -D $(EMULATOR) -O1
+
+ifeq ($(ARCH), x86_64)
+GLOBAL_CFLAGS += -mcmodel=large -m64
+else ifeq ($(ARCH), riscv64)
+GLOBAL_CFLAGS += -mcmodel=medany -march=rv64imac -mabi=lp64
+endif
+
+ifeq ($(DEBUG), DEBUG)
+GLOBAL_CFLAGS += -g 
+endif