Fix build error on WSL2

[keigo1216]

rm -f kernel/alloc.o kernel/ipc.o kernel/kernel.o kernel/print.o kernel/process.o kernel/timer.o kernel/trap.o common/common.o user/shell.o user/user.o common/common.o kernel.elf shell.elf shell.bin shell.bin.o kernel.dump *.map *.nm *.dump
cc -std=c11 -Wall -O0 -g3 --target=aarch64-none-elf -march=armv8-a -ffreestanding -nostdlib  -Ikernel  -Icommon  -Iuser   -c -o kernel/alloc.o kernel/alloc.c
cc: error: unrecognized command-line option '--target=aarch64-none-elf'
make: *** [<builtin>: kernel/alloc.o] Error 1

[keigo1216]

${CLANG}を${CC}にするとうまくいったよ

https://qiita.com/mizcii/items/cfbd2aa17f6b7517c37f