feat: create libkos crate with core modules (syscall, alloc, rt)

crates/libkos/src/rt.rs

@@ -0,0 +1,21 @@
+// Architecture-specific entry points.
+// To add a new architecture: add a cfg block with the appropriate global_asm.
+
+#[cfg(all(target_arch = "riscv64", target_os = "none"))]
+core::arch::global_asm!(
+    r#"
+.section .text.entry
+.globl _start
+_start:
+    call main
+    li a7, 16
+    ecall
+    j _start
+"#
+);
+
+#[cfg(target_os = "none")]
+#[panic_handler]
+fn panic(_: &core::panic::PanicInfo) -> ! {
+    crate::syscall::exit();
+}