lib: c: implement runtime initialisation

lib/libc/runtime/x86_64/crt0.s

@@ -3,18 +3,20 @@
 .global _start
 .type _start, @function
 
-.extern main
-.type main, @function
+.extern __libc_init
+.type __libc_init, @function
 
 .extern task_exit
 .type task_exit, @function
 
 _start:
-	# Args (as provided by the ABI)
-	# %rdi: int argc
-	# %rsi: const char **argv
-	# %rdx: kern_handle_t task
-	# %rcx: kern_handle_t address_space
+	# %rdi: (struct rosetta_bootstrap *)bs_info
+	mov %rdi, %rbx
+	call __libc_init
+
+	mov 0(%rbx), %rdi # argc
+	mov 8(%rbx), %rsi # argv
+	mov 24(%rbx), %rdx # envp
 	call main
 
 	mov %rax, %rdi