[libj6] Move _init_libc to _init_libj6

As part of the move of jsix-specific code from libc to libj6, all the
library initialization is now libj6-specific, so move it all over.

src/libraries/libc/arch/x86_64/crt0.s

@@ -1,17 +1,15 @@
 extern main
 extern exit
-extern _init_libc
+extern _init_libj6
 
 global _start:function (_start.end - _start)
 _start:
 	mov rbp, rsp
 	mov rdi, rsp
-
-	call _init_libc
+	call _init_libj6
 
 	pop rdi
 	mov rsi, rsp
-
 	call main
 
 	mov rdi, rax

src/libraries/libc/arch/x86_64/init_libc.c

@@ -1,41 +0,0 @@
-#include <stdint.h>
-#include <j6/init.h>
-#include <j6/types.h>
-
-static size_t __initc = 0;
-static struct j6_init_value *__initv = 0;
-
-j6_handle_t __handle_sys = j6_handle_invalid;
-j6_handle_t __handle_self = j6_handle_invalid;
-
-void
-_get_init(size_t *initc, struct j6_init_value **initv)
-{
-	if (!initc)
-		return;
-
-	*initc = __initc;
-	if (initv)
-		*initv = __initv;
-}
-
-void
-_init_libc(uint64_t *rsp)
-{
-	uint64_t argc = *rsp++;
-	rsp += argc;
-
-	__initc = *rsp++;
-	__initv = (struct j6_init_value *)rsp;
-
-	for (unsigned i = 0; i < __initc; ++i) {
-		if (__initv[i].type == j6_init_handle_other &&
-			__initv[i].handle.type == j6_object_type_system) {
-			__handle_sys = __initv[i].handle.handle;
-		}
-		else if (__initv[i].type == j6_init_handle_self &&
-			__initv[i].handle.type == j6_object_type_process) {
-			__handle_self = __initv[i].handle.handle;
-		}
-	}
-}

src/libraries/libc/module.toml

@@ -7,7 +7,6 @@ deps = ["j6"]
 sources = [
 	"arch/x86_64/_Exit.s",
 	"arch/x86_64/crt0.s",
-	"arch/x86_64/init_libc.c",
 	"ctype/isalnum.c",
 	"ctype/isalpha.c",
 	"ctype/isblank.c",