sys: add userspace bootstrap program

sys/bootstrap/arch/x86_64/layout.ld

@@ -0,0 +1,18 @@
+ENTRY(_start)
+
+SECTIONS {
+	.text ALIGN(4K) : {
+		*(.text)
+		*(.rodata)
+	}
+
+	.data ALIGN(4K) : {
+		*(.data)
+		*(.bss)
+	}
+
+	/DISCARD/ : {
+		*(.interp)
+		*(.dynamic)
+	}
+}

sys/bootstrap/arch/x86_64/start.S

@@ -0,0 +1,15 @@
+.code64
+
+.global _start
+.type _start, @function
+
+.extern main
+.type main, @function
+
+.extern exit
+.type exit, @function
+
+_start:
+	call main
+1:	pause
+	jmp 1b